System for distending body tissue cavities by continuous flow irrigation

ABSTRACT

The present invention provides a system and a method for distending a body tissue cavity of a subject by continuous flow irrigation such that minimal or negligible fluid turbulence is present inside the cavity, such that any desired cavity pressure can be created and maintained for any desired outflow rate. The present invention also provides a method for accurately determining the rate of fluid loss, into the subject&#39;s body system, during any endoscopic procedure without utilizing any deficit weight or fluid volume calculation or flow rate sensor. The system and the methods of the present invention described above can be used in any endoscopic procedure requiring continuous flow irrigation few examples of such endoscopic procedures being hysteroscopic surgery, arthroscopic surgery, trans uretheral surgery, endoscopic surgery of the brain and endoscopic surgery of the spine.

FIELD OF INVENTION

The present invention relates to a system for distending body tissuecavities of subjects utilizing continuous flow irrigation duringendoscopic procedures. The present invention also provides a method fordistending a body tissue cavity of a subject by continuous flowirrigation such that minimal or negligible fluid turbulence is presentinside the cavity, such that any desired cavity pressure can be createdand maintained for any desired outflow rate. The present inventionfurther provides a method for accurately determining the rate of fluidloss, into the subject's body system, during any endoscopic procedurewithout utilizing any deficit weight or fluid volume calculation or flowrate sensor. The system and the methods of the present inventiondescribed above can be used in any endoscopic procedure requiringcontinuous flow irrigation few examples of such endoscopic proceduresbeing hysteroscopic surgery, arthroscopic surgery, trans uretheralsurgery (TURP), endoscopic surgery of the brain and endoscopic surgeryof the spine.

BACKGROUND OF THE INVENTION

Endoscopic Surgery:

Endoscopic surgery is becoming increasingly popular because of thefollowing reasons:

-   (a) it is a minimally invasive form of surgery,-   (b) it avoids large incisions over the skin and muscle,-   (c) it is associated with less pain,-   (d) there is a relatively less requirement of blood transfusions and-   (e) the patients can return back to normal work relatively early    with minimal loss of working days.

While in the corresponding open conventional surgeries a relativelylarge body part consisting of skin and muscle needs to be cut in orderto gain access to an underlying body tissue cavity, in endoscopicsurgery instead of cutting body structures like skin and muscle anendoscope is introduced into the body cavity via the natural opening ofa cavity, if such exists, or alternatively a minute hole is made in thewall of the cavity through which the endoscope is introduced tovisualize the interior of the body tissue cavity and to perform major orminor endoscopic surgical procedures. For this reason endoscopic surgeryis also sometimes called ‘key hole’ or ‘minimal access surgery’. Besidesreducing the pain associated with surgery, endoscopic surgery also helpsin reducing the medical expenses.

Endoscopic Surgery is Primarily Related to a Tissue Cavity:

All endoscopic surgeries are carried out on a existing body cavity whichis distended or ‘ballooned up’ by a suitable distending apparatus whichpermits the inner lining of the said tissue cavity to be visualized bythe help of an endoscope. Though multiple endoscopic procedures havebecome established as the preferred surgical modality but still there isimmense scope of increasing the safety and efficiency of the suchexisting endoscopic procedures by improving upon the existing techniquesand apparatus used for distending body tissue cavities. Hysteroscopy,arthroscopy, TURP (transuretheral resection of the prostate), endoscopicsurgery of the brain and endoscopic surgery of the spine are few of theroutinely performed endoscopic procedures and the organs related to suchsurgeries being uterus, human joints, bladder, brain and the spinerespectively. The list of endoscopic surgeries is long, ever increasingand there is hardly any body organ or organ system to which the benefitsof endoscopy have not been extended.

Tissue Cavity is Initially Collapsed in its Natural State:

In the natural state tissue cavities are collapsed structures and thecavity walls are in apposition with each other as if kissing each other.Thus if an endoscope is introduced in such a collapsed cavity noendoscopic visualization is possible unless the cavity is ballooned upby filling it with a transparent fluid or a gas. Such ballooning of atissue cavity is technically termed as ‘cavity distension’. Noendoscopic procedure can be performed without an efficient cavitydistending system and no endoscopic procedure should be attemptedwithout a safe distending system because unsafe tissue cavity distendingmeans can lead to extreme human morbidity and even the death of apatient and such grim realities shall be discussed in the later sectionsof this manuscript. Cavity distension provides both endoscopicvisualization and mechanical distension which is necessary for themovement of endoscopic instruments.

Continuous Flow Irrigation:

In the present invention, the Inventors are focussed on a system fordistending body tissue cavities for those endoscopic procedures in whichthe cavity needs to be distended by utilizing continuous flow irrigationonly. Here, the term ‘continuous flow irrigation’ means that fluidsimultaneously enters and escapes from a tissue cavity via separateentry and exit points, as a result of which a positive fluid pressure iscreated inside the tissue cavity which distends the cavity.

The Need for Continuous Flow Irrigation:

Any tissue cavity can be easily distended in a ‘static manner’ by simplypushing fluid via a single inflow tube inserted into the cavity and inthis manner a desired cavity pressure can be developed and alsomaintained. For example, a cavity can be distended by pressing on thepiston of a simple syringe filled with fluid with the outlet end of thesyringe being connected to the cavity by a tube. Alternatively a fluidfilled bottle may be elevated to a suitable height and under theinfluence of gravity fluid from such bottle may be allowed to enter thecavity via a tube connecting the said bottle to the cavity and in thismanner a desired static pressure can be developed and also maintained.Though it is very easy to achieve distension by the said static manner,it is not a practical solution because blood and tissue debris which areinvariably released from the fragile cavity inner lining mix with thedistending fluid and endoscopic vision gets clouded within a few secondsor a few minutes. Thus continuous flow irrigation is needed toconstantly wash away blood and tissue debris in order to maintainconstant clear endoscopic vision.

Cavity Pressure and Cavity Flow Rate:

It is obvious that cavity fluid pressure and the flow rate through thecavity are the two basic parameters associated with all continuous flowirrigation systems.

An Efficient Distending System:

The Inventors believe that an efficient distending system is the onewhich provides a predictably continuous clear visualization and apredictably stable mechanical stabilization of the cavity walls. Inorder to achieve this the Inventors believe that a suitable stableconstant precise cavity pressure and a suitable stable precise cavityflow rate have to be created and maintained in a predictable andcontrolled manner. The cavity pressure should be adequate so that visionis not clouded by oozing of blood and enough mechanical separation ofthe cavity walls occurs to allow the movement of the endoscope.Similarly, the cavity flow rate should be adequate enough to constantlywash away blood and tissue debris in order to allow clear vision.

A Safe Distending System:

An efficient distending system as explained in the previous paragraphneed not also be a safe distending system. In this regard, the Inventorswould like to highlight that if the cavity pressure rises above theprescribed safe limits excessive fluid intravasation may occur or thecavity may even burst. Fluid intravasation is a process by which theirrigation fluid enters into the patient's body system through thecavity walls and may cause significant danger to the patient's lifeincluding death. This phenomenon of fluid intravasation has beenseparately discussed under the heading “Danger of fluid intravasation inhysteroscopy”. Thus a safe distending system is one which prevents orminimizes fluid intravasation and does not allow accidental mechanicalrupture of the tissue cavity.

No Prior Art is Absolutely Safe:

Many different types of uterine distending systems are known and arebeing commercially marketed by many different companies but none ofthese systems can be considered to be absolutely safe for the patient.This fact has been clearly stated in the ‘Hysteroscopic Fluid MonitoringGuidelines proposed by the Ad Hoc Committee on Hysteroscopic FluidGuidelines of the American Association of Gynecologic LaproscopistsFebruary 2000 (refer to reference 1 that is Loffler F D, Bradley L D,Brill A I et al: Hysteroscopic fluid monitoring guidelines. The journalof the Americal Association of Gynecologic Laproscopists 7(1): 167-168,1994) where the authors clearly and explicitly state “fluid pumps forlow-viscosity media are a convenience and do not guarantee safety”. Thepresent invention aims at providing a distending system which is bothsafer and more efficient in comparison to all the prior art systems.

Basic Physics of Cavity Distension:

Although, a person skilled in the art may know it, the Inventors wouldlike to provide a brief description of the basic physics of cavitydistension. Filling the tissue cavity with fluid enables distension ofthe same. Initially more fluid is pumped in than the amount which isextracted from the cavity and ultimately the inflow rate is fixed at alevel where a somewhat desired cavity pressure and distension isachieved. It may be possible to accurately maintain the desired pressureand distension in the case of a rigid cavity, for example a cavity madeof steel.

However, the body tissue cavities are not rigid because they aredistensible and also have some element of elasticity. Thus a distendedtissue cavity in its attempt to constantly revert back to its naturalcollapsed state reacts by exhibiting physiological contractions of thecavity wall which generally leads to variations in the cavity pressurewhich ultimately culminates in irregular movement excursions of thecavity walls. In a static system the said movement excursions may be sominute that they may even go unnoticed. However in a dynamic system suchthat being created during an endoscopic procedure, the saidphysiological cavity wall contractions may cause the cavity to expel outits entire fluid content thus leading to a surgically dangerous largemagnitude movement excursion of the cavity wall. Because of thesereasons it is extremely difficult to maintain the cavity pressure andcavity distension in a predictably stable fashion.

Further, the inflow tube, the out flow tube and the endoscope alsoinvariably move and shake during surgery which leads to variations influid flow resistance which is also manifested in the form of variationsin the cavity pressure. The cavity pressure variations occurring as aresult of cavity wall contractions and the mechanical movement of thetubes and the endoscope tend to occur again even if they are correctedonce because it is impossible to prevent the physiological cavity wallcontractions and the mechanical movements of the irrigation circuit.Thus, the said cavity pressure variations shall continue to occur evenafter multiple repeated corrections.

Thus, till date the surgeon was only left with two options, either toignore the said cavity pressure variations by not correcting them, or toexternally and actively correct such pressure variations. The Inventorshave noticed that any attempt to externally and actively correct thesaid cavity pressure variations leads to an undesirable turbulenceinside the cavity and also tends to amplify the resultant movementexcursions of the cavity walls. Thus there is a grave need to provide asystem which can maintain an almost constant and stable cavity pressureeven in the presence of the said physiological cavity contractions andthe mechanical movements in the irrigation circuit.

BRIEF DESCRIPTION OF AN ENDOSCOPE

Prior to describing the basic layout of a continuous flow irrigationsystem the basic structure of an ‘endoscope’ needs to be described.Endoscope is a cylindrical tube having an outer diameter ranging between3 to 9 mm approximately. A typical endoscope has four channels. Onechannel is meant to pass a fibereoptic telescope while endoscopicinstruments are negotiated through a second instrument channel. A thirdchannel also known as the inflow channel is used for pushing irrigationfluid into a tissue cavity, the proximal end of this channel ending in ametal adaptor known as the inflow port while the distal end of thisinflow channel opens near the tip of the endoscope. The inflow port isconnectable to an inflow tube which carries sterile irrigation fluidfrom a fluid source reservoir. A fourth channel also known as the outflow channel is meant for extracting waste fluid out of the cavity, theproximal end of this channel ending in a metal adaptor known as theoutflow port while the distal end of this outflow channel opens near thetip of the endoscope. The outflow port is connectable with an outflowtube which transports the waste fluid from the cavity to a suitablewaste fluid collecting reservoir. A set of fiber optic bundles containedinside the telescope transmit light energy produced by an external lightsource. This light energy illuminates the walls of the tissue cavity.The image thus formed is carried via a separate set of optical pathwaysagain situated inside the telescope. A video camera attached to the eyepiece of the telescope forms a clear endoscopic image of the cavity on aTV monitor. The endoscopic surgeon has to continuously look at the TVmonitor all through the endoscopic procedure.

Basic Layout of a ‘Continuous Flow Irrigation System:

Henceforth in this manuscript unless otherwise specified the term‘distension’ shall be deemed to imply tissue cavity distension by‘continuous flow irrigation’ only and the term ‘cavity’ unlessspecifically stated shall be deemed to refer to a ‘body tissue cavity’.In a typical distension system a physiological non viscous liquid like0.9% normal saline, 1.5% glycine, mannitol, ringer's lactate and 5%dextrose is stored in a sterile fluid source reservoir. A fluid supplytube connects the said fluid reservoir with the inlet end of an pump.The outlet end of the inflow pump is connected to the inflow port of anendoscope. When the inflow pump operates the fluid from the fluid sourcereservoir is sucked via the fluid supply tube and the inflow pump pushesthis fluid into the tissue cavity via the said inflow tube. The pumpoperates by consuming certain amount of energy and as a result of this apositive fluid pressure is created inside the tissue cavity. An outflowtube extends between the outflow port and the inlet end of an outflowpump. When the outflow pump operates it actively extracts waste fluidfrom the cavity again at the expense of energy and this waste fluid isultimately sent to a waste fluid reservoir via a tube which connects theoutlet end of the outflow pump with the waste fluid reservoir.Alternatively the outflow pump may be missing and in such case theoutflow tube directly carries the waste fluid from the cavity to thewaste fluid reservoir and the energy for such act is supplied by gravityinstead of the outflow pump. Also, the inflow pump may be missing and insuch case the inflow tube directly supplies the irrigation fluid from afluid source reservoir to the cavity. In such case the fluid sourcereservoir is hung at a suitable height above the patient and the saidenergy for cavity distension is derived from gravity instead of theinflow pump. A suitable pressure transducer is attached to the inflowtube, the outflow tube or directly to the cavity to measure the fluidpressure. A controller may be incorporated to regulate the system.

The Simplest Continuous Flow Irrigation System:

In its simplest form, a continuous flow irrigation system comprises afluid reservoir bottle hung at a suitable height above the patient andan inflow tube connecting this fluid reservoir to a tissue cavity. Anout flow tube is incorporated to remove fluid from the tissue cavity. Inthis system there is no pump and no transducer. In such a system fluidflows from the fluid source reservoir into the cavity and the requiredenergy is supplied by gravity. The pressure developed inside the cavitycan be increased or decreased by elevating or lowering the height of thefluid source reservoir. In such system the main limiting factor is theheight of the room ceiling beyond which the fluid reservoir cannot beraised. This is a crude system having negligible practical importanceand has been included only from the academic point of view. Also in sucha system unlimited volume of irrigation fluid may enter into thepatient's blood circulation. Thus such system is not suitable even fromthe patient safety point of view.

Basic Components of a Continuous Flow Irrigation System:

Like a motor car is made up of certain obvious components like engine,tyres and a steering wheel, a continuous flow distending system is madeof components like pump, pressure transducer, flow regulating valve,rubber tubes and a controller. The pump may be a positive displacementpump like a peristaltic pump, piston pump or a gear pump oralternatively it may be a dynamic pump like a centrifugal pump. Furtherthe said pump may be of a fixed RPM type which runs at fixed RPM allthrough the endoscopic procedure or the pump may be of a variable RPMtype which operates at variable RPM during the endoscopic procedure. Itis extremely important to note that fixed RPM pumps and variable RPMpumps are two separate mechanical entities in context with a cavitydistending system because the fixed and variable RPM pumps impartdifferent surgical efficiency and patient safety criteria to thedistending system. The said pump may be attached on the inflow sideonly, on the outflow side only or both on the inflow and outflow side.Further if a pump is attached only on the inflow side the outflow tubemay directly empty in a waste fluid reservoir at atmospheric pressure ora vacuum source may also be additionally attached. In some distendingsystems a flow controlling valve is attached on the outflow tube inorder to regulate the cavity pressure. There may be a single pressuretransducer attached to the inflow tube, the outflow tube or directly tothe cavity. In some systems instead of one pressure transducer twopressure transducers may be used, one on the inflow tube and the otheron the outflow tube.

Prior Art Documents Categorized According to Type of Pump Used:

Some of the prior art systems use a peristaltic pump on the inflow sidewhile the outflow tube directly drains into a waste collecting reservoirat atmospheric pressure or a vacuum source is attached to it andexamples of such systems are seen in U.S. Pat. No. 4,650,462 (DeSatanicket al), U.S. Pat. No. 4,998,914 (Weist et al), U.S. Pat. No. 5,460,490(Carr et al) and U.S. Pat. No. 6,159,160 (Hsei et al). Some examples ofsuch commercial products are Hamou Endomat (Karl Storz, Tuttinglheim,Germany), Hamou Hysteromat (Karl Storz, Tuttinglheim, Germany), UteromatFluid Control of Olympus company, Hystero Pump II 222 of Richard Wolfcompany, Arthropump (Karl Storz, Tuttinglheim, Germany) and ApexUniversal Irrigation System of Linvatec Corporation.

In one of the prior art documents, U.S. Pat. No. 5,152,746 (Atkinson etal) a piston pump has been incorporated on the inflow side while theoutflow tube simply drains into a waste collecting reservoir atatmospheric pressure.

In U.S. Pat. No. 5,814,009 (Wheatman) a pneumatic pump situated oninflow side inflates a bladder with air, wherein inflation of saidbladder exerts a force against the supply of fluid to deliver fluidthere from and the product is commercially marketed as Dolphin II FluidManagement System by ACMI CIRCON. In this system the outflow tubedirectly empties into a waste collecting reservoir at atmosphericpressure or with a vacuum source attached to it.

In some prior art such as U.S. Pat. No. 5,464,391 (DeVale) and U.S. Pat.No. 6,436,072 (16, 2002 Kullas et al) a centrifugal pump is present onthe inflow side while outflow tube may directly drain into a wastecollecting reservoir at atmospheric pressure or with a vacuum sourceattached to it.

In U.S. Pat. No. 5,630,798 (Beiser et al) a centrifugal pump is presenton the inflow side and a gear pump is installed on the over outflowside. A commercial product Intelijet System (Smith & Nephew Dyonics Inc,USA) meant for arthroscopy utilizes a centrifugal pump on the inflowside. In one prior art described in U.S. Pat. No. 5,503,626 (1996) theforce of gravity is used in the place of an inflow pump while aperistaltic pump is attached on the outflow side. In some prior artsystems two peristaltic pumps have been used, one on the inflow side andthe other on the outflow side and the examples of such prior art beingU.S. Pat. No. 4,261,360 (Perez), U.S. Pat. No. 5,556,378 (Storz et al),U.S. Pat. No. 5,246,422 (Favre) and U.S. Pat. No. 4,902,276 (Zakko).However the prior art related to U.S. Pat. No. 5,246,422 simply providestwo peristaltic pumps in a compact confined space and no operatingfunction has been proposed, while the prior art related to U.S. Pat. No.4,902,276 is meant for a non endoscopic procedure of dissolving gallstones by using two peristaltic pumps which operate intermittently inforward and backward directions and the pressure in the gall bladder ismaintained by the opening and closing of multiple valves incorporated inthe irrigation circuit. These two prior arts contained in U.S. Pat. Nos.5,246,422 and 4,902,276 are in not related to the proposed invention butthey have been included as references only because in the proposedinvention also two peristaltic pumps have been used. The contents ofthis paragraph have been summarized in table 1 which is as follows:TABLE 1 A peristaltic A peristaltic A peristaltic pump on pump on thepump on the Two peristaltic pumps A centrifugal the inflow side and a Apneumatic One pistin inflow outflow one on inflow and one pump on thegear pump on the out pump on pump on the Prior Art side side on theoutflow side inflow side flow the inflow inflow side U.S. Pat. NumbersYes 4650462, 4998914, 5460490, 6159160, Hamou Endomat (Storz), HamouHysteromat (Storz), Uteromat Fluid Control (Olympus), Hystero Pump II222 (Richard Wolf), Arthropump (Storz) and Apex Universal IrrigationSystem (Linvatec) U.S. Pat. No 5503626 Yes U.S. Pat. No 4261360, Yes5556378, 5246422 4902276 U.S. Pat. No 5464391, Yes 6436072 U.S. Pat. No5630798 Yes U.S. Pat. No 5814009 Yes U.S. Pat. No 5152746 Yes Presentinvention YesPrior Art Documents Categorized According to Fixed or Variable Pump FlowRate:

The flow rate of a positive displacement pump like a peristaltic, pistonor gear pump is proportional to the pump RPM. In some prior arts aninflow peristaltic pump works at variable flow rate via a pressurefeedback mechanism all through the endoscopic procedure. Henceforth inthis manuscript any positive displacement which works at a variable flowrate as just described shall be referred to as a ‘variable flow ratepump’ and any positive displacement pump which works at a constant flowrate through the endoscopic procedure shall be referred to as a ‘fixedflow rate pump’. Examples of ‘a variable flow rate peristaltic pump’ onthe inflow side are seen in prior arts such as U.S. Pat. No. 4,998,914(Weist et al), U.S. Pat. No. 5,460,490 (Carr et al) and U.S. Pat. No.6,159,160 (Hsei et al) and in some commercial products like HamouEndomat (Karl Storz, Tuttinglheim, Germany), Hamou Hysteromat (KarlStorz, Tuttinglheim, Germany), Uteromat Fluid Control of Olympuscompany, Hystero Pump II 222 of Richard Wolf company, Arthropump (KarlStorz, Tuttinglheim, Germany) and Apex Universal Irrigation System ofLinvatec Corporation. An example of a fixed flow rate peristaltic pumpon the inflow side is seen in U.S. Pat. No. 4,650,462 (DeSatanick et al)and in this system an adjustable flow controlling valve over outflowcontrols the cavity pressure via a pressure feedback mechanism. Anexample of a fixed flow rate peristaltic pump on the outflow is seen inU.S. Pat. No. 5,503,626 (Goldrath). An example of a variable flow rateperistaltic pumps on the inflow and on the outflow sides is seen U.S.Pat. No. 1,261,360 (1, 1981, Perez). An example of a fixed flow rateperistaltic pump on the inflow side and a variable speed peristalticpump on the outflow side is seen in U.S. Pat. No. 5,556,378 (Storz etal). Henceforth in this manuscript a centrifugal pump which operates atvariable RPM under the influence of a pressure feedback mechanism shallbe referred to as ‘variable RPM centrifugal pump’. Examples of ‘variableRPM centrifugal pump’ on the inflow side are seen in U.S. Pat. No.5,464,391 (DeVale) and U.S. Pat. No. 6,436,072 (Kullas et al). Anexample of a system having a ‘variable RPM centrifugal pump’ on theinflow and a ‘fixed flow rate’ gear pump on the outflow is seen in U.S.Pat. No. 5,630,798 (Beiser et al). A summary of this paragraph is givenin table 2 which is as follows: TABLE 2 categorizing the prior art onthe basis of variable and fixed flow rate pumps: Fixed flow A variableRPM Fixed Variable rate peristaltic centrifugal pump Flow rate Avariable A fixed A fixed flow rate pump on the A variable on the inflowperistaltic flow rate flow rate flow rate peristaltic inflow and a RPMand a fixed pumps peristaltic peristaltic peristaltic pumps on thevariable flow rate centrifugal flow rate gear on the inflow pump pump onpump on inflow and peristaltic pump pump on pump on and on the Prior Arton the inflow the inflow the outflow outflow on the outflow the inflowthe outflow out flow U.S. Pat Nos 4998914, Yes 5460490, 6159160 HamouEndomat (Storz), Uteromat Fluid Control (Olympus), Hystero Pump II 222(Richard Wolf), Arthropump (Storz), Apex Universal Irrigation System(Linvatec) U.S. Pat No 4650462 Yes U.S. Pat No 5503626 Yes U.S. Pat No4261360 Yes U.S. Pat No 5556378 Yes U.S. Pat Nos Yes 5464391, 6436072U.S. Pat No 5630798 Yes The present invention YesPrior Art Documents Categorized on the Basis of Adjustable FlowControlling Valve on the Outflow Tube:

In some prior arts such as U.S. Pat. No. 4,650,462 (DeSatanick et al)and U.S. Pat. No. 5,460,490 (Carr et al) an adjustable flow controllingvalve on the outflow tube is used for regulating the cavity pressure.

Before describing the physical principals of some of the important priorart systems and their drawbacks, hysteroscopic surgery, TURP surgery andArthroscopic surgery shall be briefly described especially in contextwith fluid intravasation, the importance of constant clearvisualization, the importance of cavity wall stabilization and therelevance of physiological cavity wall contractions. The concepts ofreducing cavity refilling time, intraoperatively switching between twodifferent types of irrigation fluids and predicting the required volumeof irrigation fluid shall also be described.

Hysteroscopic Surgery:

In the word hysteroscopy ‘hyster’ means the uterus and ‘scopy’ meansvisualization, thus the term hysteroscopy meaning visualization of theof the uterine cavity. The uterus is also commonly known as the woman'swomb. Hysteroscopy is a very useful technique as diagnoses and treats alarge number of gynecologic diseases without the need of removing thewoman's womb. Some common hysteroscopic procedures are TCRE (TransCervical Resection of the Endometrium which is commonly also referred toas ‘endometrial resection’), fibroid resection, polyp resection,adhesiolysis, septoplasty, hysteroscopic tubal cannulation and visuallytargeted endometrial biopsy. Procedures like septolpasty, sub mucousfibroid resection and visually guided adhesiolysis can be accomplishedonly by hysteroscopic means and in such procedures utilization of theold conventional open surgical techniques may be considered illogicaland may also invite medico legal action.

Anatomy of the Uterus:

The uterus is a hollow pear shaped organ having an approximately 5 mm to20 mm thick muscular wall which encloses the uterine cavity. In a youngnulliparours woman the uterus measures about 8 cm in the long length,about 5 cm in the transverse diameter and about 5 cm in the anteroposterior axis. The hollow cavity present inside the uterus is known asthe uterine cavity. The uterine cavity opens into the vagina via itsnatural opening known as external os. During hysteroscopy the uterinecavity is distended by pushing fluid through the natural opening of theuterus. The uterine cavity is lined by a 2 to 6 mm thick, delicate andfragile, tissue membrane known as the endometrium. The fertilized eggimplants over the endometrium and subsequently a completely developedfetus is delivered through the natural opening of the uterus.

Cavity Distension in Hysteroscopy:

The uterine cavity can be distended by pushing fluids or carbon dioxidegas into the cavity. Carbon dioxide gas has a limited use in fewdiagnostic procedures while the major hysteroscopic procedures requirethe uterine cavity to be distended only by continuous flow irrigation.Thus the use of gas has largely been abandoned in favor of physiologicalnon viscous liquids like 0.9% normal saline, 1.5% glycine, mannitol,ringer's lactate and 5% dextrose. Proper distension of the uterinecavity is the primary requirement for safe and accurate completion ofall hysteroscopic procedures. Uterine distension, if not done properly,may lead to dangerous surgical complication like fluid overloadresulting from excess fluid intravasation (see references 2,3 i.e.Olsson J et. al, “Early detection of the Endometrial Resection Syndrome”Gynecol Obstet Invest 42: 142-4, 1996 and Roesch R P et. al, “Ammoniatoxicity resulting from glycine absorption during a transuretheralresection of the prostrate” Anesthesiology 58: 577-79, 1983) and othercomplications like uterine perforation.

Fluid overload may culminate in the patient's death by a process knownas TUR syndrome.

Need for Continuous Flow Irrigation in Hysteroscopy:

While performing hysteroscopic surgery, an endoscope is first insertedinto the uterine cavity. Next, fluid is pushed into the uterine cavityvia an inflow tube attached to the inflow port of an endoscope. Due tothe resultant accumulation of fluid the uterine cavity distends and anendoscopic image of the uterine cavity is seen on a TV monitor. Theinner lining of the uterine cavity, technically known as theendometrium, is a very delicate membrane which readily bleeds even onbeing minutely touched by the endoscope or during surgery and thisreleased blood causes clouding of endoscopic vision because blood beingopaque impairs the passage of light. Thus, in order to maintain a clearvision the dirty blood mixed fluid from the uterine cavity by constantlyreplacing with fresh clear fluid by the said process of ‘continuous flowirrigation’. ‘Continuous flow irrigation’ is thus a method of distendinga tissue cavity in such a manner that fluid is continuously instilledinto the cavity, while an equal amount of fluid is being constantlyremoved out of the cavity.

The Need of Maintaining Predictably Almost Constant Precise UterineCavity Pressure:

In hysteroscopic surgery and in all other related surgeries utilizingcontinuous flow irrigation it is extremely important to a maintainpredictably almost precise constant cavity pressure all through thesurgery because a predictably stable cavity pressure helps in attaininga predictably stable mechanical stabilization of the cavity walls.

Minimum Turbulence is Desirable:

In the nature of the fluid flow through the cavity is turbulent tissuedebris shall continuously float in the cavity in an irregular fashionthus obstructing visualization and it also decreases the mechanicalstabilization of the cavity walls by encouraging irregular cavity wallmovement excursions. Thus, the cavity fluid turbulence should berelatively less and preferably should be reduced to almost negligiblelevels.

Fluid Pressure Should be Independent of the Flow Rate:

In technical terms it should be possible to create and maintain anydesired precise tissue cavity pressure for desired constant outflow rateincluding a zero outflow rate. This statement an be alternatively statedby saying that cavity pressure has to be made absolutely independent ofthe cavity flow rate. In hysteroscopic surgery it is essential to have adistending system in which four different types of combinations between‘cavity pressure’ and ‘cavity flow rate’ can be achieved and suchcombinations are described in table 3 which is as follows: TABLE 3 ADESIRED RELATION BETWEEN CAVITY DISADVANTAGES OF PRESSURE AND CAVITYADVANTAGES OF SUCH A SUCH A FLOW RATE RELATIONSHIP RELATIONSHIP Lowcavity pressure at low Reduces the overall volume of Adequate distensionmay flow rate fluid intravasation and also not be achieved, bloodreduces the risk of an accidental may ooze and tissue debris excessfluid intravasation may not be removed quickly Low cavity pressure athigh Reduces the overall volume of Adequate distension may flow ratefluid intravasation and helps in not be achieved, blood quick evacuationof tissue may ooze debris and blood High cavity pressure at low Helps inattaining a better The overall volume of flow rate mechanical distensionof the intravasation may be cavity, helps in preventing relatively highoozing of blood by pressure temponande and reduces the risk of anaccidental excess fluid intravasation High cavity pressure at high Helpsin attaining a better The overall volume of flow rate mechanicaldistension of the intravasation may be cavity, helps in preventingrelatively high and the risk oozing of blood through of an accidentalexcess pressure temponande and helps fluid intravasation may in quickevacuation of tissue also be relatively high debris and blood(Note: The concepts of ‘fluid intravasation’ and ‘accidental excessfluid intravasation’ have been described in the next two paragraphs).

The surgeon may need to switch between the said four combinationsmultiple times in the same endoscopic procedure. The said fourcombinations between pressure and flow rate need to be utilized in otherendoscopic procedures utilizing continuous flow irrigation also such asTURP and arthroscopy. In the present invention besides many otherbenefits the said four combinations between pressure and flow rate arepossible to achieve, because in the present invention the cavitypressure is made absolutely independent of the cavity flow rate.

Danger of Fluid Intravasation in Hysteroscopy:

In continuous flow irrigation the rate at which the fluid enters intothe uterine cavity via the inflow tube is known as the inflow rate whilethe rate at which fluid escapes from the uterine cavity via the outflowtube is known as the outflow rate. As a result of continuous flowirrigation a positive pressure develops due to which the uterine cavitydistends. Normally a cavity pressure of 50 to 100 mm Hg pressure issufficient to distend the uterine cavity. In some hysteroscopicprocedures like ‘endometrial resection’ multiple small blood vessels arecut and the pressure in the lumen of such cut blood vessels may be aslow as 5 mm Hg while the intrauterine pressure usually ranges between 50to 100 mm Hg, thus a positive pressure gradient always exists betweenthe uterine cavity and the lumen of the cut blood vessels. In accordancewith the known laws of physics, under the influences of the saidpressure gradient the pressurized cavity fluid constantly enters intothe systemic circulation of the patient via the said cut ends of theblood vessels and such process is commonly termed as ‘fluidintravasation’. In case of an accidental mechanical rupture of theuterine cavity wall (uterine perforation) the cavity fluid enters intothe abdominal cavity (peritoneal cavity) through the perforation site.The intravasation rate in the case of uterine perforation can be veryhigh, as the pressure inside the abdominal cavity is very low, almostequal to the atmospheric pressure. In most major hysteroscopicprocedures ‘1.5% glycine fluid’ is used to distend the uterine cavityhowever excess intravasation of such fluid may be dangerous as it leadsto an increase in the circulating blood volume (hypervoluemia), adecrease in the blood osmolarity (hypoosmolarity) and a reduction in theblood sodium ion concentration (hyponatremia) all of which combinedtogether constitute a clinical syndrome known as TUR syndrome which mayeven culminate in the patient's death. TUR syndrome is so named as thissyndrome was initially observed in TURP surgery which is a similarprocedure like hysteroscopic endometrial resection. It is to be notedthat in TURP also multiple small blood vessels are cut as in endometrialresection. It is important to know and limit the volume of theintravasated fluid to as minimum as possible, as excessive absorption ofany type of irrigation fluid is dangerous and may even culminate inmortality.

Increased Inflow Rate Increases the Risk of Accidental ExcessIntravasation in Hysteroscopy:

In continuous flow irrigation fluid enters the cavity at some flow ratewhich commonly termed as the ‘inflow rate’ while simultaneously fluidescapes from the cavity at some flow rate commonly termed as the‘outflow rate’ and as a result of these two processes a positive fluidpressure developed inside the cavity. As stated in the previousparagraph the pressure inside the venous blood vessels and inside theabdominal cavity is very low thus if large diameter veins areaccidentally cut or if a perforation occurs then almost the entire fluidwhich is entering the cavity via the inflow tube can enter into thepatient's blood circulation or into the abdominal cavity. Henceforth inthis manuscript the maximum flow rate at which the irrigation fluid mayenter into the patient's body system shall be termed as the ‘maximumpossible intravasation rate’. Thus the ‘maximum possible intravasationrate’ is almost equal to the maximum possible or permissible inflowrate. Both positive displacement pumps such peristaltic pumps and thedynamic pumps such as centrifugal pumps carry the risk of high ‘maximumpossible intravasation rate’. As explained in the subsequent paragraphunder the heading “Centrifugal Pump on the Inflow” in the systems havinga peristaltic pump on the inflow side the ‘maximum possibleintravasation rate’ is reduced or limited by fixing the maximum RPMbeyond which the pump cannot operate but this is usually achieved at theexpense of reducing the value of the maximum cavity pressure which thesystem can generate. In the systems which incorporate a centrifugal pumpon the inflow side the ‘maximum possible intravasation rate’ is highbecause in centrifugal pumps the pump flow rate and the pressure headare related in a parabolic manner. In the eventuality of an accidentlike cavity perforation the pump outflow rate becomes very high becausethe pressure head may becomes almost zero. In centrifugal pumps the‘maximum possible intravasation rate’ can be reduced or limited byfixing the maximum RPM beyond which the centrifugal pump cannot operatebut again this is achieved at the expense of reducing the value of themaximum cavity pressure which the system can generate. This has beenexplained in the same paragraph. Hypothetically assuming an inflow rateof 500 ml/minute, in such a situation, the patient can absorb up to 5liters of fluid in just 10 minutes, which in all probability wouldculminate in the patient's death. Thus it would be definitely much saferto use a uterine distending system in which the cavity pressure could beincreased and maintained at any desired value without increasing theinflow rate and without allowing the inflow rate to increase at anytime.

Measurement of Instantaneous Real Time Rate of Fluid IntravasationIncreases Patient Safety:

According to the ‘Hysteroscopic Fluid Monitoring Guidelines proposed bythe Ad Hoc Committee on Hysteroscopic Fluid Guidelines of the AmericanAssociation of Gynecologic Laproscopists (see reference 1) fluidabsorptions greater than 750 ml may be dangerous to the patient's life.In many prior art systems the total volume of fluid absorbed into thepatient's body is determined by substracting the volume or weight ofwaste fluid present in a waste fluid collecting reservoir from thevolume or weight of the sterile irrigation fluid which was initiallypresent in the fluid source reservoir and a average rate ofintravasation is calculated by dividing the determined fluid deficit bythe total time taken for the said intravasation to occur. In this mannerthe magnitude of rate of intravasation is assessed only after thecomplication of intravasation has occurred and such system does notprovide the safety of preventing intravasation from occurring. In theeventuality of an excessive intravasation having occurred the surgeoncan only treat the patient to the best of his abilities but the despitesuch efforts there can be significant morbidity or even mortality. Insome prior art systems efforts have been made to determine the volume ofintravasated fluid by measuring the weight of the fluid in the fluidsource reservoir and the weight of the fluid present in a waste fluidcollecting vessel and subtracting the latter weight from the formerweight. The just stated method of determining the volume of fluidintravasation are described in prior arts such as U.S. Pat. No.5,492,537 (Vancaillie), U.S. Pat. No. 5,556,378 (Storz et al), U.S. Pat.No. 5,814,009 (Wheatman), U.S. Pat. No. 5,921,953 (Novak) and U.S. Pat.No. 5,503,626 (Goldrath). However if the instantaneous real time rate offluid intravasation is constantly known all through surgery thennecessary preventive actions, including abandoning the surgery, can betake by the surgeon within a few seconds after sudden increase in therate of intravasation is detecting and in this manner the dangerouscomplication of excess fluid intravasation can be prevented fromoccurring. The instantaneous rate of fluid intravasation can bedetermined by incorporating one fluid flow rate sensor on the inflowtube and one fluid flow rate sensor on outflow tube and subtracting theflow rate value of the outflow sensor from the flow rate value of theinflow sensor. Theoretically this appears to be a simple task butpractically it is very difficult, especially in context with endoscopicsurgery where reliability, accuracy and sterility are importantcriteria. Many types of external or internal flow rate sensors workingon mechanical or electromechanical principals are known as of today buttheir accuracy and reliability, especially where the irrigation fluid isnon viscous and transparent in nature, is a debatable issue. Thus in thesaid context only that sensor can be permitted to be used which isabsolutely reliable and very accurate because a malfunction orinaccurate measurement of the said sensor may culminate in patientmorbidity or even mortality. In German Patent No. 4417189 A1 (MeyerEdgar et al.) a mechanical flow rate sensor has been proposed to beincorporated inside the lumen of the inflow tube to determine the inflowrate while the outflow rate is determined by noting the flow rate of aperistaltic pump installed on the outflow side. It is also to be notedthat any flow sensor which is installed inside the lumen the irrigationtubes also poses considerable practical difficulties with respect tomaintaining a sterile bacteria free environment. Thus it is highlydesirable to have a system of reliably and accurately determining theinstantaneous real time rate of fluid intravasation withoutincorporating any kind of flow rate sensor either inside or outside thelumen of the irrigation tubes, however such a system is not present inany of the prior art systems. Thus the Inventors believe that it wouldbe beneficial to continuously and in a reliable and accurate manner todetermine the real time rate of fluid intravasation without using anykind of fluid flow rate sensor.

The Significance of the Actual Cavity Pressure in Hysteroscopy:

As already stated previously fluid intravasation occurs due to apositive pressure gradient which inadvertently exists between thepressurized cavity fluid and the lumen of the cut blood vessels,especially the veins. Thus, any increase in the uterine cavity pressureincreases the rate of fluid intravasation by promoting the entry of theirrigation fluid through the cut ends of the blood vessels. There aretwo types of blood vessels, veins and arteries. While the blood pressureinside the veins is as low as 5 mm Hg the blood pressure inside thearteries may be as high as 100 mm Hg. Considering a hypotheticalsituation where the pressure inside an artery being 100 mm Hg, thepressure inside a vein being 5 mm Hg and the uterine cavity pressurebeing 80 mm Hg. In such situation, if both veins and arteries are cutthe blood oozes out through the arteries while the pressurizedirrigation fluid enters into the veins through their cut ends. If largerdiameter veins are accidentally cut intravasation may occur at adangerously high rate and the literature has many case reports in whichmortalities occurred due to such accidents. Usually the surgeons do notlike increase the uterine cavity pressure beyond the mean arterialpressure of the patient, but such maneuver is only possibly if theactual cavity pressure is known. In order to avoid excess intravasationthe surgeon works at the minimum allowable intrauterine pressure atwhich there is no bleeding and the cavity is also adequately distendedto allow free movement of endoscopic instruments. Fluid intravasationbeing directly related to the cavity pressure it is becomes essentialfor the surgeon to know the actual pressure which exists inside theuterine cavity. The actual cavity pressure can be measured by directlyplacing a pressure transducer inside the cavity or by inserting acatheter directly into the cavity with a transducer being attached atthe distal end of the catheter such that the transducer measures a truestatic pressure, but such maneuvers are tedious and practicallydifficult. In many prior art systems a pressure transducer is attachedat the upstream part of the inflow tube but such transducers may read apressure which is higher than the actual cavity pressure due tomechanical frictional imposed by the inner surface of the inflow tube tothe moving fluid column, a phenomenon which has been explained in detailin subsequent paragraphs. Further the cavity wall also exhibitsphysiological contraction movements which causes the cavity pressure tofluctuate in an irregular fashion and such pressure fluctuations areovercorrected or under corrected by the prior art systems which makes iteven more difficult to determine the actual cavity pressure. Theirrigation pipes and the endoscope are also constantly moving or shakingwhich continuously varies the overall resistance to fluid flow thusleading to fluctuations in the cavity flow rate which again causes incavity pressure fluctuations. In the prior systems as described in U.S.Pat. No. 4,998,914 (Weist et al) and U.S. Pat. No. 5,556,378 (Storz etal) the cavity pressure determined by considering flow resistance, flowrate and the sensed pressure.

The Need of Predictably Continuous Clear Visualization in HysteroscopicSurgery:

A predictable and continuous clear visualization is extremely essentialfor all types of hysteroscopic procedures but the importance of clearvision shall be explained especially in context with EndometrialResection which is a classical representative of major hystroscopicprocedures. Endometrial resection is performed in those women who sufferwith excess blood loss during their menstrual periods and this procedureis an extremely physiological alternative to hysterectomy (removal ofthe uterus) because in endometrial resection the uterus is not needed tobe removed form the woman's body. Thus it is thus an organ conservingsurgery. It is to be noted that each year lakhs of women undergohysterectomy and endometrial resection can avoid hysterectomy in manysuch cases. In this procedure the entire inner lining of the uterinecavity, the endometrium, is cut electrosurgically along with an adequatethickness of the underlying myometrium. Myometrium is the muscular wallof the uterine cavity and the roots of the endometrial glands penetrateinto the myometrium to variable depths ranging from 1 to 4 mm but insome situations like adenomyosis the endometrial glands may be seenpenetrating deeper up to 10 mm or even more. Considering a hypotheticalcase in which most endometrial glands penetrate up to a depth of 3 mmwhile few glands are found to be growing much deeper into themyometrium. If such deep penetrating glands are not removed duringendometrial resection they may again regenerate and the patient mayagain develop the initial disease of excessive menstrual bleeding. Thusit is important to either completely remove or destroy all theendometrial glands and in order to accomplish this the surgeon has toprecisely identify and target the openings of such glands beforeelecrtrosurgically cutting such glands to the required depth, whilesimultaneously coagulating the cut ends of large diameter blood vesselsif encountered, talking extreme care to avoid a blood hemorrhage orexcess intravasation. Any accidental deep cut into the myometrium atthis stage may lead to a life threatening fluid intravasation or ahemorrhage. Such precision and fine surgery is only possible if apredictably continuous clear endoscopic vision is available all throughsurgery. In the absence of clear visualization accidents like cavitywall perforation can also occur. The importance of continuous clearvision cannot be over emphasized and it is one of the most importantrequirements for safety and efficiency for every endoscopic surgicalprocedure.

The Need of Cavity Wall Stabalization in Hysteroscopic Surgery:

As already stated, the uterine cavity wall exhibits physiologicalcontraction movements which produce variations in the cavity pressurebut such pressure fluctuations are amplified on being constantlycorrected by the prior art systems which culminates into significantundesirable movement excursions of the cavity wall. Further theirrigation pipes and the endoscope are also constantly moving or shakingwhich produces minute variations in the overall resistance to fluid flowwhich causes minute fluctuations in the cavity pressure which is alsocorrected, over corrected or under corrected as just stated and furtherads to the magnitude of the resultant cavity wall movement excursion.Let us take a hypothetical example where the intramural part of thefallopian tube is being cut during a procedure of endometrial resection.The total cavity wall thickness around the intramural part of thefallopian tube is about 2 mm, thus a cavity wall movement excursion of 3mm shall lead to the perforation of the cavity wall which may culminateinto a serious injury as high voltage electrosurgical currents are alsoused in the process. Thus it is highly desirable to mechanicallystabilize the cavity wall and to limit the magnitude of cavity wallmovement excursions to as minimum as possible, however such movementscannot be totally eliminated.

The Concept of Reducing Cavity Refilling Time:

In hysteroscopic surgery and in many other endoscopic surgeries likeTURP the resectoscope needs to be withdrawn multiple times during theendoscopic procedure either to remove the resected tissue pieces or inorder to change the operating instruments. Each time the resectoscope isremoved the entire cavity fluid spills out of the cavity and when theresectoscope is reintroduced it takes time for the cavity to againcompletely fill up with fluid and the magnitude of such time dependsupon the cavity volume capacity and the inflow rate. For example in TURPsurgery the urinary bladder having a substantially high volume capacity,about 300 ml, the time taken for the bladder to completely fill is alsorelatively high. A similar situation is seen in a large size uteruswhere the cavity volume may be high. Thus a lot of valuable surgicaltime is wasted in repeatedly filling the cavity with fluid becauseduring the cavity refilling phase definitive surgery cannot be done asproper visualization may not be available in a partially filled cavity.The time taken for an empty cavity to completely fill up with theirrigation fluid shall henceforth be referred to as the ‘cavityrefilling time’ and the time phase in which the cavity is being filledshall being termed as the ‘cavity refilling phase’. If the ‘cavityrefilling time’ is somehow reduced the total surgical time can besignificantly shortened. In the present invention besides many otherbenefits the said ‘cavity refilling time’ can be varied, that decreasedor increased, by any desired magnitude in a predictably controlled andsafe manner.

Intraoperatively Switching Between Two Types of Irrigation Fluids:

In routine practice, at the beginning of an endoscopic procedure thesurgeon chooses a suitable type of irrigation fluid. As alreadymentioned in the above paragraph physiological non viscous liquids like0.9% normal saline, 1.5% glycine, mannitol, ringer's lactate and 5%dextrose are used for distending tissue cavities. Such fluids have beentermed ‘physiological’ as their use is permitted in endoscopic surgerieshowever all said fluids are not totally physiological in the true senseof the meaning because absorption of such fluids does lead tophysiological imbalances and even mortality if absorbed in excess.However certain fluids like 0.9% normal saline are considered relativelymore physiological than some fluids like 1.5% glycine. Ionic fluids like0.9% normal saline and ringer's lactate, being isotonic and isoosmolarwith respect to blood, are considered relatively more physiological incomparison to the non ionic fluids like 1.5% glycine, mannitol and 5%Dextrose which are hypotonic and hypoosmolar with respect to blood.Henceforth the term normal saline shall imply a 0.9% normal salinesolution and the term glycine shall imply 1.5% glycine because fluids ofsuch concentrations are routinely used as irrigation fluids. Theosmolarity and sodium ion concentration of blood plasma is 290 mosmol/Land 137 milli equivalent/L respectively, while the osmolarity and sodiumion concentration of 0.9% normal saline solution is 308 mosmol/L and 154milli equivalent/L respectively. Thus even if an excess volume of normalsaline is absorbed into the systemic circulation it does not causehyponatremia (decrease in sodium concentration) or hypoosmolarity(decrease in osmolarity). However excess absorption of normal saline maylead to hypervolemia (an increase in the circulating blood volume) whichis relatively less dangerous complication when compared to hyponatremiaand hypoosmolarity and can corrected in a short time by administeringintravenous diuretics. It is for this reason that 0.9% solution ofsodium chloride is the fluid of first choice whenever the surgicalprocedure permits its use. On the other hand the osmolarity of 1.5%glycine solution is only 200 mosmol/L and it is totally deficient insodium ions. Hence excess absorption of 1.5% glycine leads to acomplication known as TUR syndrome as it was first observed in TURP. TURsyndrome comprises of mainly three types of physiological imbalancesnamely hyponatremia, hypoosmolarity and hypervolemia. If the patientdevelops TUR syndrome the water from the circulating blood enters intothe brain and lung cells and the patient may die due to resultant brainedema and lung edema, besides many other physiological aberrations beingcaused. However the use of 1.5% glycine fluid is a necessary evil ascertain underwater monopolar electrosurgical procedures can only becarried out by using such non ionic fluids. Also, the severity ofphysiological imbalance caused by glycine absorption is directly relatedto the total volume of glycine absorbed. Normal saline is aphysiologically safer to use but it cannot be used in those surgicalprocedures which utilize monopolar electrosurgery as in endometrialresections and prostate resections where monopolar electrosurgery isutilized to cut the diseased tissue. Sodium ions make normal saline agood conducter of electricity. For this reason monopolar electrosurgerycannot be done by using normal saline because the sodium ions dissipatethe electrical energy in all directions which does not allow the entiremonopolar electrical energy to pass through a specific target locationwhich in turn does not allow production of localized intense heat bywhich tissue is cut in monopolar electrosurgical procedures. 1.5%Glycine being deficient in sodium ions does not conduct electricity thusintense heat can be concentrated at a target point during monopolarelectrosurgical procedures. On the other hand certain bipolar underwaterelectrosurgical procedures, like those done with the help of a bipolarversapoint generator, can be carried out only in the presence of sodiumions present in normal saline because in such procedures heat energy canbe localized at the tip of an electrode only in the presence of sodiumions. Thus if monopolar electrosurgery is contemplated then non ionicfluids like 1.5% glycine are chosen at the beginning of the surgery. Incase no electrosurgery is contemplated or a bipolar underwater type ofelectrosurgery is contemplated then ionic fluids like normal saline arechosen at the beginning of the endoscopic procedure. However duringsurgery situations may arise which require changing from an ionic fluidto a non ionic fluid and vice versa, for example switching betweennormal saline and glycine or vice versa. Few such situations arementioned as follows:

-   1. If at the beginning of the procedure electrosurgery is not    contemplated then normal saline is chosen, but if after the    introduction of the endoscope an intracavitatory pathology is seen    which needs to be treated by monopolar electrosurgery then it is    necessary to change from normal saline to glycine.-   2. If at the beginning of the endoscopic procedure no electrosurgery    is contemplated or if underwater type of bipolar surgery is    contemplated then normal saline is initially chosen, however if an    intracavitory pathology is subsequently discovered which needs to be    treated by monopolar electrosurgery then the initially taken normal    saline has to be replaced by glycine in order to carry out monopolar    electrosurgely.-   3. In certain endoscopic procedures like endometrial resection which    utilize monopolar electrosurgery glycine is used for cavity    distension. In such procedures considerable time may be spent in    removing the resected tissue pieces under endoscopic vision by    grasping mechanically with the cutting loop and during such maneuver    unnecessararily an extra volume of glycine is absorbed into the    patient's body. If during such time while the tissue pieces are    being taken out glycine is substituted by normal saline then    relatively less glycine is absorption for the same total volume of    fluid absorbed and this causes a relatively lesser harm to the    patient because in such case a considerable part of the absorbed    fluid consists of a relatively more quantity of the more    physiological normal saline fluid.

Switching between two types of irrigation fluids as mentioned aboveessentially requires that the entire fluid present in the irrigationcircuit consisting of the inflow tube and the tissue cavity is replacedby flushing with a second type of irrigation fluid. The fluid initiallychosen at the beginning of surgery is being referred to as the ‘firstfluid’ and the later chosen fluid by which the irrigation circuit needsto be flushed is being referred to as the ‘second fluid’. The degree ofcontamination of the second fluid by the molecules of the first fluid isbeing termed as the ‘purity’ of the second fluid, the second fluid beingconsidered 100% pure if it has no molecules of the first fluid presentin it but such situation cannot be attained practically. Considering afirst hypothetical situation where normal saline being the first fluidneeds to be replaced by glycine as the second fluid, in such a case theflushing of the irrigation circuit has to continue till the purity ofthe second fluid glycine reaches a threshold level at which the degreeof contamination of second fluid glycine by sodium ions is so less thatfor all practical purposes the second fluid glycine does not conductelectricity and the said threshold level of purity can be determinedexperimentally. Practically even with rigorous flushing it may not bepossible to have a zero concentration of sodium ions in the second fluidglycine thus flushing is done only to the extent that the purity of thesecond fluid glycine is increased to the said minimum threshold level atwhich the electrical conductivity of the second fluid glycine is lowenough to allow monopolar electrosurgery to be carried out. The timetaken for such flushing to be completed is being termed as the ‘flushingtime’. In physical terms the said flushing is achieved by instilling thesecond fluid through the inflow tube while the first fluid is allowed toescape through the out flow tube and such process is continued till thedesired purity threshold level is achieved in the second fluid glycine.Now considering a second hypothetical situation in which the first fluidglycine needs to be replaced by the second fluid normal saline in orderto permit bipolar electrosurgery, in such case the process of flushingis continued till the concentration of the second fluid normal salineincreases to a minimum threshold concentration of sodium ions at whichbipolar electrosurgery is possible to performed. In the just mentionedfirst and second hypothetical situations the required flushing timedecreases if the flushing flow rate during the flushing phase isincreased. A low flushing time is highly desirable as the surgeon doesnot have to wait unduly long for the process of flushing to complete. Ashort flushing time thus shortens the total surgical time. However arelatively shorter flushing time requires that the second fluid shouldflow through the inflow tube and the tissue cavity at a suitably highflow rate during the flushing phase but such high fluid flow rate maycreate a dangerously high pressure inside the tissue cavity. If theflushing time can be shortened without increasing the cavity pressurethen such maneuver of shortening the flushing time can be very helpfulin endoscopic procedures like endometrial resection, TURP andarthroscopy as it empowers the surgeon to minimize the patient'sexposure to a relatively less physiological fluids and it also allowsthe surgeon to choose between different types of irrigation fluidsduring the same endoscopic procedure. Thus a system is desired in whichthe flushing time can be reduced in a desired controlled manner bytemporarily increasing the flow rate through the irrigation circuit suchthat the cavity pressure does not change during such maneuver.

Predicting the Total Volume of Required Irrigation Fluid:

In endoscopic procedures the irrigation fluid to be used in surgery isusually contained in fluid bottles which are hung on a stand oralternatively the irrigation fluid is kept inside a sterile fluid sourcecontainer. If the irrigation fluid finishes during surgery it wastessubstantial valuable surgical time while a fresh supply of theirrigation fluid is replaced and during this time blood clots mightaccumulate in the cavity subsequent to the loss in cavity distension.Such clots have to be removed because they impair visualization, thusmaking surgery difficult and longer. It is difficult to remove suchclots as they may spread diffusely over the entire cavity surface. Allthis can be avoided if before starting the surgery or at any time duringthe course of surgery the total volume of irrigation fluid required tocomplete the surgery could be predicted, so that exactly the same volumeof fluid could be taken in one single attempt. By such maneuver surgeryis not disrupted at any moment on account of changing fluid bottles orthe fluid in the fluid source container. The irrigation fluid which isat room temperature has to be warmed to match the body temperature andthis takes time. Thus if the expected total requirement of irrigationfluid is known the same can be warmed to body temperature and thesurgeon shall not have to stop surgery in between while the fluid warmsto body temperature. Such a provision of predicting the total requiredfluid volume can be very helpful in endoscopic procedures likeendometrial resection and transuretheral resection of the prostate.

TURP:

TURP (Trans utretheral resection of the prostate gland) is a commonlyperformed urologic procedure which is also a classical representative oftransuretheral endoscopic procedures. TURP is a very frequentlyperformed procedure in men of the older age group who usually presentwith urinary retention due to enlargement of the prostate gland. Thegeneral principles and problems related to cavity distension are similarin TURP and hysteroscopic surgery. In TURP an endoscope is introducedthrough a natural opening known as the uretheral meatus. Uretheralmeatus is the natural opening via which urine is expelled duringmicturation. As the resectoscope is advanced through the male uretherathe prostate gland and the bladder cavity are subsequently visualizedand if the prostate gland is found enlarged it is resected electrosurgically and the surgical procedure is known as TURP. Hysteroscopicendometrial resection and TURP surgery are similar in light of the factthat in both surgeries multiple blood vessels are inadvertently cut andthe irrigation fluid has a grave potential to intravasate into thesystemic circulation through the cut end of such blood vessels, thusleading to a dangerous physiological aberration known as the TURsyndrome. The mechanism of fluid intravasation in TURP is same as inhysteroscopic surgery as explained above. Also it is clearly mentionedin Campbells Text Book of Urology 2002 (see reference 4 i.e. CampbellsText Book of Urology 2002, 8^(th) edition Edited by Patrick C Walsh page1409) that during routine TURP surgeries the patient can absorb fluid atan alarming rate of 20 ml/minute. Thus it is important to know the realtime rate of fluid intravasation in TURP surgery as well. Multiplereferences of the dangers of fluid intravasation in TURP surgery arefound in the literature. All the features related to continuous flowirrigation discussed in context with hysteroscopic surgery are equallyrelevant in context with TURP surgery also and in order to avoidrepetition the same is not being discussed again.

Arthroscopy:

Arthroscopy means visualization of the joint cavity. The basicprincipals of cavity distension in arthroscopy, hysteroscopy and TURPsurgery are almost similar. All the features related to continuous flowirrigation discussed in context with hysteroscopic surgery are equallyrelevant in context with arthroscopic surgery also and in order to avoidrepetition such features shall not be again discussed. A predictablyconstant clear visualization, a predictably stable mechanicalstabilization distension of the joint cavity and maintenance of jointcavity pressure totally independent of the outflow rate are fewimportant requirements for safe and efficient arthroscopic surgery. InCampbells Text Book of Operative Orthopeadics 2003 (see reference 5 i.e.Campbells Text Book of Operative Orthopeadics 2003, 10^(th) edition,Volume 3, Edited by S Terry canale, page 2504) it is clearly mentionedthat proper distension of the joint cavity is essential for any type ofarthroscopic viewing and the problems of fluid extravasation are alsoclearly highlighted. In arthroscopic surgery the irrigation fluid canescape into the tissues surrounding the joint and such complication istermed as fluid extravasation. Thus fluid extravasation which occurs inarthroscopy is similar to the ‘fluid intravasation’ which is observed inhysteroscopy and TURP with the difference between the two being that‘intravasation’ is a broad term while ‘extravasation’ related to fluidwhich diffuses into the tissues surrounding a tissue cavity. Thus inthis manuscript the term ‘intravasation’ shall also be deemed to includethe phenomenon of ‘extravasation’. The extravasated fluid compresses theblood vessels which results in a reduced blood supply to vitalstructures like motor or sensory nerves which may temporarily orpermanently damage the nerves. Thus fluid extravasation is one the majorcomplications of arthroscopy. The real time evaluation of the rate ofintravasation (extravasation in the case of arthroscopy) which is aunique feature of the present invention can be very helpful in avoidingor minimizing fluid extravasation during arthroscopy. Arthropump plus(Karl Storz, Tuttinglheim, Germany) is a popular prior art system usedfor distending the joint cavities in arthroscopy it is not surprising tonote that the basic mechanics and working principals of this pump aresimilar to a uterine distending pump Hamou Endomat (Karl Storz,Tuttinglheim, Germany). Thus it is seen that the basic mechanics and theworking principals of the pumps used in arthroscopic surgery fordistending joint cavities is similar to the pumps used in hysteroscopicsurgery for distending the uterine cavity. Some other commerciallyavailable pump systems for use in arthroscopy are Arthro Pump 2202 ofRichard Wolf, the Intelijet and Access 15 systems of Dyonics and theApex Universal Irrigation System of Linvatec Corporation. Some otherprior art devices used in arthroscopy are described in U.S. Pat. No.4,650,462 (DeSatanick et al), U.S. Pat. No. 4,998,914 (Weist et al),U.S. Pat. No. 5,556,378 (Storz et al), U.S. Pat. No. 6,436,072 (Kullaset al), U.S. Pat. No. 5,460,490 (Carr et al) and U.S. Pat. No. 5,152,746(Atkinson et al).

A Proposed Definition for an Ideal ‘Continuous Flow IrrigationDistending System’:

On the basic of the complications and the general principals associatedwith ‘continuous flow irrigation’ the Inventors propose here belowdefine an ideal continuous flow irrigation distending system. TheInventors believe that in order to become ideal systems, a continuousflow irrigation distending system should comprise of 16 features whichare as follows:

-   1. It should be possible to use the same distending system in all    endoscopic surgeries which utilize ‘continuous flow irrigation’.-   2. A predictably constant clear visualization should always be    available.-   3. A predictably stable distension of the cavity walls should always    be present.-   4. The physiological contractions of the cavity wall should have    negligible or minimal effect on the cavity pressure and cavity    distension.-   5. The mechanical movements of the irrigation tubes and the    endoscope should have negligible or minimal effect on the cavity    pressure and cavity distension.-   6. The real time rate of intravasation of the irrigation fluid    should be constantly known to the surgeon without using any type of    fluid flow meters.-   7. It should be possible to create and maintain any desired cavity    pressure for any desired constant flow rate at which fluid may be    allowed tb pass through the cavity.-   8. An almost actual fluid pressure inside the cavity should always    be known to the surgeon in a simple and reliable manner, while    working at any flow rate, without the need of inserting a separate    catheter into the cavity and by using a pressure sensor situated far    away from the cavity in the upstream portion of the inflow tube.-   9. Negligible or minimal fluid turbulence should be present in the    fluid inside the cavity and in the fluid flowing through the rest of    the irrigation circuit, thus implying that the fluid flow should be    as close to a streamline flow as possible.-   10. The pressure difference between any two points situated in the    endoscopic irrigation circuit should be negligible or minimal even    at high flow rates encountered in endoscopic surgery. Also at a    fixed cavity flow rate the pressure difference between any two fixed    points in the irrigation circuit should not vary during the entire    endoscopic procedure.-   11. It should be possible to maintain a relatively higher cavity    pressure without increasing the ‘maximum possible intravasation    rate’.-   12. It should be possible to increase or decrease the cavity    refilling time in a predictably controlled manner.-   13. It should be possible to predictably limit the magnitude of a    pressure surge which might occur if the outflow tube is accidentally    blocked especially while working at a high flow rate.-   14. It should be possible to predict by a fair degree of accuracy    the total volume of irrigation fluid which would be consumed in the    entire endoscopic procedure so that required quantity of irrigation    is fluid is taken at the beginning of surgery so that surgery is not    interrupted later on account of changing the fluid bottles.-   15. It should be possible to safely, easily and quickly switch    between two different types of irrigation fluids, for example    between normal saline and glycine, intraoperatively during an    endoscopic procedure, in any desired short period of time such that    the cavity pressure does not vary as a result of such maneuver.-   16. It should be possible to set an upper safe limit for the maximum    permissible cavity pressure and the maximum permissible inflow rate    and it should be possible to set these two safety parameters    independent of each other.

In the preceding paragraphs the physical principals, the components andsurgical complications associated with ‘continuous flow irrigation’ havebeen explained in context with endoscopic procedures such ashysteroscopy, TURP and arthroscopy. Also multiple prior art systems havebeen categorized on the basis of component layout. In the subsequentparagraphs the physical principals, advantages and disadvantages of theprior art systems shall be described to establish the uniqueness, themechanical novelty and the functional novelty of the present inventionin comparison to the prior art systems.

A Variable Speed Peristaltic Pump on Inflow:

Hamou Endomat (Karl Storz, Tuttinglheim, Germany) is a populardistending system and is used by surgeons worldwide for distending theuterine cavity in hysteroscopic surgeries. In this system a peristalticpump is incorporated on the inflow side of the uterine cavity while theout flow tube directly drains into a waste fluid collecting vessel atatmospheric pressure and a provision of attaching a vacuum source to thesaid waste fluid collecting vessel is also provided in this system. Apressure transducer located in the upstream portion of the inflow tubeconstantly senses the fluid pressure and constantly conveys feedbackpressure signals to a controller which in turn regulates by a feed backmechanism the rotations of the peristaltic pump, thereby constantlyincreasing or decreasing the pump flow rate in order to maintain thecavity pressure around a desired value. Thus the cavity pressure is notconstant and fluctuates around the initially preset value. The cavitypressure thus exhibits irregular fluctuations having a variablefrequency and variable amplitude. Such pressure fluctuations do notpermit a constantly clear visualization as it does not allowestablishment of a stable mechanical distension of the cavity walls.Prior to starting the endoscopic procedure the surgeon selects desiredvalues of the maximum permissible cavity pressure and the maximumpermissible inflow rate for the planned endoscopic procedure and thesaid values are fed into a controller via suitable input means providedin the pump system console. In such system the ‘desired cavity pressure’and ‘the value of the maximum permissible cavity pressure’ both are thesame entities. Let a hypothetical situation be assumed wherein thesurgeon selects 80 ml/min as the maximum inflow rate and 100 mm Hg asthe desired that is maximum permissible cavity pressure. When the systemis started the peristaltic pump operates at increasing RPM's to create100 mm Hg pressure, however if even at the maximum set inflow rate of 80ml/min also a cavity pressure lower than 100 mm Hg is developed then theperistaltic pump just continues to work at the said maximum flow rate of80 m/min even though the cavity pressure continues to remain below thedesired value of 100 mm Hg. In such situation the cavity pressure can beraised to desired preset value of 100 mm Hg only by increasing the valueof the maximum permissible inflow rate or by reducing the magnitude ofoutflow suction. The outflow being essentially uncontrolled, reducingthe out flow vacuum also may not yield the desired result, at least notin a predictable or controlled manner. The purpose of having includingthe just stated hypothetical situation is to demonstrate that in theHamou Endomat, the cavity pressure is not independent of the flow rate,such that the cavity pressure can be increased or decreased bycorrespondingly increasing or decreasing the inflow rate. Also, in theHamou Endomat if the maximum permissible inflow rate is increased italso increases the ‘maximum possible intravasation rate’, a conceptwhich has already been explained. Also as explained above thephysiological contractions of the cavity wall and the unavoidablemovements of the irrigation tubes and the endoscope gives rise to minutepressure variations inside the cavity. Such pressure variations areconstantly corrected by the said system which causes significantpressure fluctuations in the uterine ca ity. An uncontrolled outflow isone of the major reason due to which a predictably stable cavitypressure and a predictably stable cavity wall distension cannot bemaintained by the Hamou Endomat distension system. Taking an extremeexample, by using the Hamou Endomat, it is impossible to maintain aprecise cavity pressure of 100 mm Hg for a precise cavity flow rate of 1ml/min, while such extreme situation is very easily possible if thesystem of the present invention is used. The features available in thesystem of Hamou Endomat is compared with the ideal system as definedabove by the Inventors to find its suitability in Table 4. TABLE 4Comparison of the System of Hamou Endomat with the Ideal System IDEALSYSTEM SYSTEM OF HAMOU ENDOMAT It being possible to create and maintainany desired Not possible. precise tissue cavity pressure for any desiredprecise constant outflow rate for any length of time. The instantaneousreal time rate of fluid Only the total volume of fluid intravasationinto the patient's body being absorbed over a certain period of timeconstantly known without using any type of fluid can be determined. Theinstantaneous flow rate sensors. real time rate of fluid intravasationis not obtainable. It being possible to maintain the cavity pressure atNo, the cavity pressure continuously any desired precise value for anylength of time. fluctuates around a preset value. It being possible tomaintain any desired high cavity Not possible. pressure withoutincreasing the ‘maximum possible intravasation rate’. It being possibleto predictably maintain a constant Not possible. clear visualization anda stable cavity distension for any length of time. It being possible toeasily and quickly change over Not possible. from one type of irrigationfluid to a different type of irrigation fluid intra operatively duringan endoscopic procedure in any desired short period of time such thatthe cavity pressure does not change during such maneuver.* Examples of some other prior art systems similar to ‘Hamou Endomat’are Uteromat Fluid Control of Olympus company, Hystero Pump II 222 ofRichard Wolf company, Arthropump plus (Karl Storz, Tuttinglheim,Germany) and a system described in U.S. Pat. No. 4998914 (Weist et al).A Variable Speed Peristaltic Pump on Inflow & a Flow Regulating Valve onOutflow:

Systems manufactured by Apex Universal Irrigation System (LinvatecCorporation, USA) for use in arthroscopic surgery has been described inU.S. Pat. No. 5,460,490 (Carr et al). The physical principals of thissystem are similar to the Hamou Endomat (Karl Storz) described in theprevious paragraph except for the fact that a pressure regulating pinchvalve has been attached over the out tube. By reducing the lumen of theoutflow tube by constricting the said pinch valve relatively higherjoint cavity pressures can be achieved for the same inflow rates. Byincorporating the said pinch valve an attempt has been made to make thecavity pressure relatively independent of the cavity flow rate. Howeverat any one position of the pinch valve the cavity pressure can only beincreased by increasing the rotations of the inflow peristaltic pump.The features available in the system of Apex Universal Irrigation System(Linvatec) is compared with the ideal system as defined above to findits suitability in Table 5. TABLE 5 Comparison of the System of ApexUniversal Irrigation System with the Ideal System APEX UNIVERSALIRRIGATION IDEAL SYSTEM SYSTEM (linvatet Corporation, USA) It beingpossible to create and maintain any Not possible. desired precise jointcavity pressure for any desired precise constant outflow rate, for anylength of time. It being possible to know the instantaneous real Notpossible. time rate of fluid extravasation without using any fluid flowrate sensors. It being possible to maintain pressure at any No, thecavity pressure continuously desired precise value for any length oftime. fluctuates around a preset value. It being possible to maintainany desired high This is possible only if an upper safe limit jointcavity pressure without increasing the for the maximum inflow rate ispreset and ‘maximum possible extravasation rate’, by adequatelytightening the outflow pinch valve. It being possible to predictablymaintain a Not possible. constant clear visualization and a stablecavity distension for any length of time. It being possible to easilyand quickly change Not possible. over from one type of irrigation fluidto a different type of irrigation fluid intra operatively during anendoscopic procedure in any desired short period of time such that thecavity pressure does not change during such maneuver.A Fixed Speed Peristaltic Pump on Inflow and a Flow Regulating Valve onOutflow:

U.S. Pat. No. 4,650,462 (DeSatanick et al) describes a prior art systemsuggested to be used in arthroscopic surgery. In this system a fixed RPMperistaltic pump which operates at fixed preset flow rate isincorporated on the inflow side, a pressure transducer measures thepressure directly from the joint cavity and a variable flow controllingvalve is attached over the out flow tube. The peristaltic pumpconstantly runs at a fixed flow rate while the variable flow controllingrestriction valve by a pressure feedback mechanism maintains the cavitypressure around a desired preset value by constantly constricting anddilating the inner diameter of the outflow tube. The distal end of theoutflow tube opens in a waste collecting container with a vacuum sourceattached to it. Due to irregular opening and closing of the restrictionvalve the cavity pressure is turbulent and exhibits wide amplitudearound a preset pressure value. The frequency of the said pressurefluctuations is also irregular. The features available in the systemdescribed in U.S. Pat. No. 4,650,462 (DeSatanick et al) is beingcompared with the features that should be available in an ideal systemto find out the suitability of the system of DeSatanick et al in table6. TABLE 6 Comparison of the System of DeSatanick et al with the IdealSystem IDEAL SYSTEM DeSatanick et al It being possible to create andmaintain any desired Not possible. precise joint cavity pressure for anydesired precise constant outflow rate, for any length of time. It beingpossible to know the instantaneous real Not possible. time rate of fluidextravasation without using any type of fluid flow rate sensors. Itbeing possible to maintain the pressure at any No, the cavity pressurecontinuously desired precise value for any length of time. fluctuatesaround a preset value. It being possible to maintain any desired highjoint May be possible by fixing an upper safe cavity pressure withoutincreasing the ‘maximum limit of the inflow rate and by suitablypossible extravasation rate’. reducing the outflow tybe lumen bytightening the outflow regulating valve. It being possible topredictably maintain a constant Not possible. clear visualization and astable cavity distension for any length of time. It being possible toeasily and quickly change over Not possible. from one type of irrigationfluid to a different type of irrigation fluid intra operatively duringendoscopic procedure in any desired short period of time such that thecavity pressure does not change during such maneuver.A Fixed Speed Peristaltic Pump on the Inflow and a Variable SpeedPeristaltic Pump on the out Flow:

U.S. Pat. No. 5,556,378 (Storz et el) describes a prior art systemsuggested to be used in endoscopic surgeries such as hysteroscopy, TURPand arthroscopy. In this system two peristaltic pumps operatesimultaneously, the inflow pump pushes fluid into the tissue cavitywhile the outflow pump extracts fluid from the cavity. One pressuretransducer is located on the outlet end of the inflow pump while asecond pressure transducer is located on the inlet end of the outflowpump. The pressure signals from both these pressure transducers are sentto a controller. The RPM of each pump are determined by suitable sensorslike tachometers and the corresponding RPM signals are also sent to thecontroller. The peristaltic pump RPM are directly proportional to thepump flow rate thus the RPM related signals from both the pumps sendflow rate related information to the controller. In this system theinflow peristaltic pump constantly operates at a fixed predeterminedflow rate while the outflow peristaltic pump operates at variable flowrates under the influence of pressure feedbacks from the two pressuretransducers and the flow rate of the inflow peristaltic pump which hasalready been predetermined. Before starting the surgery the surgeonchooses a desired flow rate for the inflow peristaltic pump and adesired pressure which would be maintained inside the cavity all throughthe endoscopic procedure. On the basis of the pressure signals from thetwo pressure transducers and set flow rate of the inflow pump thecontroller maintain the cavity pressure around the preset value byconstantly increasing or decreasing the flow rate of the out flowperistaltic pump. The features available in the system described in U.S.Pat. No. 5,556,378 (Storz et al) is being compared with is beingcompared with the features that should be available in an ideal systemto find out the suitability of the system of Storz et al in table 7.TABLE 7 Comparison of the System of Storz et al with the Ideal SystemIDEAL SYSTEM U.S. Pat. No. 5556378 (Storz et al) It being possible tomeasure the actual cavity Two pressure transducers determine thepressure in a simple and easy manner using cavity pressure in arelatively less accurate minimum number One pressure transducer inmanner because the cavity pressure the upstream part of the inflow tubeconstantly fluctuates. accurately measures the actual cavity pressure ina simple and easy manner. It should be possible to operate the systemThis system cannot be operated without the even without a controller.help of a controller. It being possible to create and maintain any Notpossible. desired precise cavity pressure for any desired preciseconstant outflow rate, for any length of time. It being possible to knowthe instantaneous Only the total volume of fluid absorbed over real timerate of fluid intravasation without a certain period of time can bedetermined. using any type of fluid flow rate sensors. It being possibleto know the real time rate of Not possible. fluid intravasation withoutusing a controller. It being possible to maintain the cavity No, thecavity pressure continuously pressure at any desired precise value forany fluctuates around a preset value. length of time. It being possibleto maintain any desired high This is possible by fixing the inflow rateat a joint cavity pressure without increasing the safe level. ‘maximumpossible extravasation rate’. It being possible to predictably maintaina Not possible. constant clear visualization and a stable cavitydistension for any length of time. It being possible to easily andquickly change Not possible. over from one type of irrigation fluid to adifferent type of irrigation fluid intra operatively during anendoscopic procedure in any desired short period of time such that thecavity pressure does not change during such maneuver.

The system of Storz is somewhat close to the ideal system. However, theInventors have noticed that it is not at all possible to operate thesystem of Storz without utilizing the controller. The controller is anintegral part of the system of Storz. Applicants have further noticedthat as the outflow pump is a variable speed peristaltic pump which iscontinuously controlled by the controller, the cavity pressurecontinuously fluctuates around a preset value. This is because of thefact that the fluctuations in the cavity pressure due to thephysiological cavity wall contractions and the mechanical movements ofthe irrigation circuit are for very short time period and are irregular.The Applicants have noticed that the pressure transducers attached onthe inflow and the outflow sides to detect the cavity pressure. Once avariation in the cavity pressure is detected, a corresponding signal issent to the controller, which after comparing the input signal with areference signal, outputs a correction signal which is provided to theoutflow pump, which thereafter corrects amount of liquid being withdrawnfrom the cavity. It may take about 2 to 4 seconds approximately for theentire process to happen and by the time the outflow pump startscorrecting, the cavity would have returned back to its original shape.Thus, the Applicants note that in the system of Storz et al thecontroller constantly corrects the variations in the cavity pressurecaused by the physiological cavity wall contractions and the mechanicalmovements of the irrigation circuit, thus extending the time period forwhich the cavity pressure varies. This leads to extended turbulenceinside the cavity.

Note: There are many more mechanical and functional differences betweenthe present invention and the system just described, that is U.S. Pat.No. 5,556,378 (Storz et al).

Centrifugal Pump on the Inflow:

A system described in U.S. Pat. No. 6,436,072 (Kullas et al) issuggested to be used in endoscopic procedures such as hysteroscopy, TURPand arthroscopy. In this system a variable RPM centrifugal pump isincorporated as the inflow pump and a pressure transducer constantlysenses the cavity pressure and sends corresponding pressure signals to acontroller. Similarly a sensing devise such as a tachometer coupled withthe rotor shaft said centrifugal pump constantly sends the pump RPMrelated information to the controller. By a pressure feedback mechanismthe controller regulates the pump RPM in such a manner that the cavitypressure is maintained around a desired predetermined value. Acentrifugal pump is a dynamic pump whose outflow rate is inherentlyinversely responsive to the pressure in the outflow circuit which inthis case is the pressure inside the tissue cavity. The basic componentlay out of the system is such that a sterile irrigation fluid containedinside a fluid source reservoir is transported to the inlet end of thecentrifugal pump via a plastic tube which connects the fluid sourcereservoir with the inlet end of the said centrifugal pump. The fluidsource reservoir is usually hung at a height about 1 to 2 feet above thepump in order to introduce fluid into the pump inlet by gravity. Beforestarting the endoscopic procedure the surgeon selects a desired cavitypressure to be maintained during the endoscopic procedure by feeding thevalue of the said desired pressure via suitable input means which arepresent in the pump console system. In system being discussed theoutflow is uncontrolled because the outflow tube directly empties into awaste fluid collecting reservoir. If the transducer senses a fall in thecavity pressure the controller increases the efficiency of thecentrifugal pump by increasing its RPM and in this manner the pumpoutflow rate is increased which ultimately culminates in an increasedcavity pressure. Similarly if an increased cavity pressure is sensed thecavity pressure is accordingly reduced by reducing the RPM of the pump.The advantage of using a centrifugal pump is that even if the pumpoutflow is totally blocked the pump outflow pressure cannot exceed acertain value commonly termed as the pressure head. In physical termsthe pressure head of a centrifugal pump is the pressure generated on thepump outflow side at a zero flow rate, a situation which can be attainedby intentionally blocking the pump outflow tube. Alternatively if thedischarge of the centrifugal pump is pointed straight up in a verticalpipe the fluid in a vertical tube shall rise to a certain maximum heightand the pressure generated at the base of such a vertical column offluid is known as the ‘pressure head’ of the centrifugal pump. The pumphead is mainly determined by the pump RPM and the outside diameter ofthe pump impeller. The pump head is increased by increasing theefficiency of the pump and the efficiency of the pump can be increasedby either increasing the pump RPM or by increasing the outside diameterof the pump impeller. The main problem associated with such centrifugalpump systems is that if the pressure head is increased by increasing theRPM then maximum possible pump flow rate, that is the pump flow rate ata zero pressure head, becomes dangerously high and this significantlyincreases the ‘maximum possible rate of fluid intravasation’. Let ahypothetical situation be considered wherein at 1000 RPM a cavitypressure of 80 mm Hg is being maintained for a cavity flow rate of 100ml/min which essentially means that in context with stated parametersthe pump is actually pumping fluid into the cavity at a rate of 100ml/min. If accidentally a large diameter vein inside the cavity wall iscut the cavity pressure may immediately drop to almost zero whichimplies that effective pressure head (that the pressure at the pumpoutflow) has also fallen to zero and at such a low pressure head thispump may push fluid into the tissue cavity at a very high rate which maybe as high as 2 to 3 litres/min and if irrigation fluid intravasatesinto the patient's blood circulation at such high rates the patient maydie within minutes. It may be argued that a maximum permissible upperlimit of the pump RPM may be set but if the desired cavity pressure isnot achieved at the said upper RPM limit then surgeon has to perform acompromised surgery at an undesired low cavity pressure or increase thecavity pressure by increasing the maximum permissible upper limit of thepump RPM but such action again increases the ‘maximum possibleintravasation rate’. Thus in such systems if the cavity pressure can beraised then the ‘maximum possible intravasation rate’ also increases.Taking an extreme hypothetical example while in the present invention itis possible to predictably and precisely maintain the cavity pressure at300 mm Hg pressure with the ‘maximum possible intravasation rate’ beingequal to 2 ml/min, such a situation in impossible to even conceive inthe centrifugal system being described in this paragraph. Further, incase of the said centrifugal pump system the cavity pressure is neverstable as it constantly fluctuates around a preset value in an irregularmanner and the fluid turbulence inside the cavity is also very high.Features of the said centrifugal pump system described in the U.S. Pat.No. 6,436,072 is being compared with the features of the ideal system intable 8. TABLE 8 Comparison of the System of Khullas et al with theIdeal System IDEAL SYSTEM U.S. Pat. No. 6436072 (Kullas et al) It beingpossible to create and maintain any desired Not possible. precise cavitypressure for any desired precise constant outflow rate, for any lengthof time. It being possible to know the instantaneous real Not possible.time rate of fluid intravasation without using any type of fluid flowrate sensors. It being possible to maintain the cavity pressure at No,the cavity pressure continuously any desired precise value for anylength of time. fluctuates around a preset value. It being possible tomaintain any desired high cavity Not possible. pressure withoutincreasing the ‘maximum possible intravasation rate’. It being possibleto predictably maintain a constant Not possible. clear visualization anda stable cavity distension for any length of time. It being possible toeasily and quickly change over Not possible. from one type of irrigationfluid to a different type of irrigation fluid, intra operatively duringan endoscopic procedure in any desired short period of time such thatthe cavity pressure does not change during such maneuver.Variable Speed Centrifugal Pump of the Inflow and a Gear Pump on theOutflow:

Such a system has been described in the U.S. Pat. No. 5,630,798 (Beiseret al) and has been suggested to be used in endoscopic procedures suchas arthroscopy. This system is similar to the system described in theabove paragraph except for the fact that in this system a ‘fixed speedgear pump’ has also been incorporated on the outflow side. The surgeonsets a desired cavity pressure and also sets a specific flow rate forthe gear pump. By a pressure feedback mechanism the controller maintainsthe cavity pressure around a desired value by constantly varying the RPMof the inflow centrifugal pump. However a precise stable cavity pressureis not achieved and the cavity pressure constantly fluctuates around apreset pressure value and the said pressure fluctuations are of anirregular frequency and irregular amplitude. However one advantage ofthis system in comparison to the system described in the previousparagraph is that in this system there is a relatively slightly bettermechanical stabilization of the cavity walls and pressure fluctuationsare also relatively less. However significant cavity pressurefluctuations and fluid turbulence do exist. In this system if the cavitypressure is increased by decreasing the RPM of the outflow gear pump the‘maximum possible rate of fluid intravasation’ does not increase becausethe in this system the ‘maximum possible rate of fluid intravasation’ isequal to the maximum outflow rate of the inflow centrifugal pump at zeropressure head which increases only if the RPM of the centrifugal pumpare increased In the presently being discussed system for a specificvalue of the centrifugal pump RPM the specific value of maximum cavitypressure can be generated by reducing the RPM of the outflow gear pumpto zero value, however if a still higher cavity pressure is requiredthen that can be possible only by increasing the RPM of the inflowcentrifugal pump which would dangerously increase the ‘maximum possiblerate of fluid intravasation or extravasation’. It has already beenstated previously that the term ‘intravasation’ is deemed to include theprocess of ‘extravasation’ as well but in this paragraph the term‘extravasation’ has been intentionally used because the prior art beingdiscussed has specifically recommended to be used in arthroscopicprocedures besides other endoscopic procedures, and in arthroscopicprocedures ‘extravasation’ predominates over ‘intravasation’ though bothterms are essentially same. It is also to be noted that in the U.S. Pat.No. 5,630,798 (Beiser et al) being discussed a gear pump has been usedas a positive displacement pump however no gear pump can be 100% sealedand some forward or backward leakage might occur while the pump isoperating or is stationary and the direction of such leakage shalldepend on the pressure gradients on both sides of the gear pump. In thisrespect a gear pump is different from a peristaltic pump, which is alsoa positive displacement pump, because in a peristaltic pump no fluidflow in any direction when the pump is stationary. The said leakagethrough a gear pump tends to make the outflow relatively uncontrolled,depending upon the magnitude of such leakage which imparts turbulence tothe fluid flow. Features of the said centrifugal pump system describedin the U.S. Pat. No. 5,630,798 (Beiser et al) is being compared with thefeatures of the Ideal system to find out its suitability in table 9:TABLE 9 Comparison of the System of Beiser et al with the Ideal SystemINDEAL SYSTEM Pat No 5630798 (Beiser et al) It being possible to createand maintain any desired Not possible. precise cavity pressure for anydesired precise constant outflow rate, for any length of time. It beingpossible to know the real time rate of fluid Such feature is not presentis this prior intravasation. art. It being possible to know theinstantaneous real Not possible. time rate of fluid intravasation evenwithout using a controller. It being possible to maintain the cavitypressure at No, the cavity pressure continuously any desired precisevalue for any length of time. fluctuates around a preset value. It beingpossible to maintain any desired high Not possible. cavity pressurewithout increasing the ‘maximum possible intravasation rate’. It beingpossible to predictably maintain a constant Not possible. clearvisualization and a stable cavity distension for any length of time. Itbeing possible to easily and quickly change over Such feature is notpresent is this prior from one type of irrigation fluid to a differenttype art. of irrigation fluid intra operatively during an endoscopicprocedure in any desired short period of time such that the cavitypressure does not change during such maneuver.The Dolphin II Fluid Management System (ACMI Circon, USA):

This type of system has been described in U.S. Pat. No. 5,814,009(Wheatman). In this system the irrigation fluid is pushed into theuterine cavity by the help of a bladder pump which compresses theirrigation fluid contained in a collapsible plastic container. In thissystem a pressure transducer located in the downstream portion of theinflow tube near the inflow port constantly senses the cavity pressureand sends appropriate signals to a controller which by a feedbackmechanism regulates the air pressure inside the bladder enclosing thesaid collapsible fluid source container. If the said pressure transducersenses a fall in the uterine cavity pressure it sends a feedback signalto the said controller via a feedback mechanism and the controller inturn increases the air pressure inside the said bladder by activating anair compressor which results in the collapsible fluid source containerbeing compressed with a greater force which culminates in an increasedinflow rate and the end result being an increased uterine cavitypressure. Similarly when the uterine cavity pressure increases thecontroller causes the bladder pressure to decrease and the end resultbeing a reduced uterine cavity pressure. In this system the cavitypressure is maintained by irregularly fluctuating around a preset value,thus implying that in the said system the pressure cannot be maintainedat a fixed and precise value. Features of the Dolphin II FluidManagement System (ACMI CIRCON) is being compared with the features ofthe ideal system to determine its suitability in table 10. TABLE 10Comparison of the System of Wheatman et al with the Ideal System IDEALSYSTEM U.S. Pat. No. 5814009 (Wheatman) It being possible to create andmaintain any desired Not possible. precise cavity pressure for anydesired precise constant outflow rate, for any length of time. It beingpossible to know the instantaneous real time Not possible. rate of fluidintravasation without using any flow rate sensor. It being possible tomaintain the cavity pressure at No, the cavity pressure continuously anydesired precise value for any length of time. fluctuates around a presetvalue. It being possible to maintain any desired high cavity Notpossible. pressure without increasing the ‘maximum possibleintravasation rate’. It being possible to predictably maintain aconstant Not possible. clear visualization and a stable cavitydistension for any length of time. It being possible to easily andquickly change over Not possible. from one type of irrigation fluid to adifferent type of irrigation fluid, intra operatively during anendoscopic procedure in any desired short period of time such that thecavity pressure does not change during such maneuver.

Thus it can be noticed that none of the system available till today orthose which have been patented do not provide all the features requiredto qualify to be called as an ideal system.

OBJECTS OF THE INVENTION

The main object of the invention is to provide a safe and efficientsystem for distending body tissue cavities for those endoscopicprocedures which utilize continuous flow irrigation. In technical termsthe user should be able to create and maintain any desired pressureinside a tissue cavity through which fluid may be allowed to flow at anydesired constant flow rate.

Another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to create andmaintain any desired precise cavity pressure for any desired precise andfixed outflow rate, for any length of time.

Still another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to achieve apredictably constant clear endoscopic vision throughout the endoscopicprocedure.

Yet another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to achieve apredictably stable mechanical cavity distension throughout theendoscopic procedure.

One more object of the present invention is to provide a system fordistending tissue cavities using which it being possible to predictablymaintain the cavity pressure at any desired precise value despitephysiological contractions of the cavity wall.

One another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to constantly,accurately and reliably determine the instantaneous real time rate offluid intravasation into the patient's body without using any type offluid flow rate sensors.

A further object of the present invention is to provide a system fordistending tissue cavities using which it being possible to determinethe instantaneous real time rate of fluid intravasation mechanicallywithout using a controller or any type of fluid flow rate sensors.

A further more object of the present invention is to provide a systemfor distending tissue cavities using which it being possible to maintainany desired precise and high cavity pressure without increasing the‘maximum possible fluid intravasation rate’.

Another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to measure theactual cavity pressure, in an accurate, reliable and simple manner, byusing a pressure transducer located far away from the cavity in the upstream portion of the inflow tube.

Yet another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to make thepressure inside the body cavity and the flow rate of the fluid passingthrough the body cavity absolutely independent of each other such thatthe value of any may be altered without affecting the value of theother.

Still another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to reduce thecavity filling time in a predictably controlled manner and at the sametime achieving a desired cavity pressure at the end of the cavityrefilling phase, cavity refilling time being the time taken tocompletely fill a cavity with the irrigation fluid.

One more object of the present invention is to provide a system fordistending tissue cavities using which it being possible for the surgeonto have a fairly accurate assessment of the total volume of theirrigation fluid which would be required to complete the entireendoscopic procedure.

On another object of the present invention is to provide a system fordistending tissue cavities using which it being possible for the surgeonto accurately know the maximum pressure which might develop inside thecavity in case of an accidental obstruction of the outflow tube and itshould be possible to minimize such rise in the cavity pressure in acontrolled and predictable manner.

A further object of the present invention is to provide a system fordistending tissue cavities using which it being possible to easily,quickly and safely change from one type of irrigation fluid to adifferent type of irrigation fluid, for example between normal salineand glycine, intraoperatively (that is during a surgical procedure), inany desired short period of time such that the cavity pressure does notchange during such maneuver.

SUMMARY OF THE INVENTION

The present invention is a safe and an efficient system for distendingbody tissue cavities for those endoscopic procedures which utilizecontinuous flow irrigation. The present invention is a system ofcreating and maintaining any desired positive pressure inside a bodytissue cavity through which fluid is made to flow at any fixed flowrate, including a zero flow rate. Alternatively the present inventionmay be considered as a system of creating cavity fluid pressure which isabsolutely independent of the cavity outflow rate. The present inventioncomprises of two peristaltic pumps which work simultaneously, forindefinite time, at absolutely fixed flow rates to create and maintainany precise desired cavity pressure for any desired cavity outflow rate,including a zero outflow rate. One pump is located on the inflow side ofa cavity while the other pump is attached to the out flow side of thecavity. Further if any fluid is being absorbed into or through thecavity walls, such as fluid intravasation which occurs duringhysteroscopic endometrial resection, the instantaneous real time rate ofsuch fluid absorption can be constantly determined in the proposedinvention without using any type of fluid flow rate sensors. Also thecavity pressure can be maintained at any desired high value withoutincreasing the ‘maximum possible fluid intravasation rate’. The proposedinvention also has multiple other features of endoscopic surgicalrelevance which greatly enhance the patient safety and efficiency duringendoscopic surgery few such features being shortening of the cavityrefilling time in a predictably controlled fashion, to be able topredict by a fair degree of accuracy the volume of fluid which would berequired to complete the endoscopic procedure, to be able to quicklyswitch during endoscopic surgery between two types of irrigation fluidswithout varying the cavity pressure and to be able to predict and limitthe magnitude of the maximum increase in the cavity pressure or themagnitude of a minor pressure surge which might occur in case of anaccidental obstruction of the outflow tube for a specific outflow rate.Also the same system can be used for all types of endoscopic procedureswhich utilize continuous flow irrigation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the basic block diagram of the invention with thecontroller system.

FIG. 2 shows the block diagram of the invention without the controllersystem.

FIG. 3 shows the inflow part of the system along with the inflowperistaltic pump 5, the pressure transducer 17 and the constriction site8.

FIG. 4 is similar to FIG. 2 except that in this figure a shaded regionrepresents an area having an almost similar pressure.

FIG. 5 shows curves 1, 2 and 3.

FIG. 6 shows curves 4, 5 and 6.

FIG. 7 shows curves 3 and 7.

FIG. 8 shows curves 8 and 9.

FIG. 9 is similar to FIG. 2 except that an additional/optionalconstriction housing tube 17 and an additional/optional pressuretransducer 18 has been included.

FIG. 10 shows the high resolution, sharp & high magnification imagesobtained using the system of the present invention.

DETAILED DESCRIPTION OF INVENTION

Accordingly, the present invention provides a system for distending bodytissue cavities of subjects by continuous flow irrigation duringendoscopic procedures the said system comprising:

a fluid source reservoir containing a non viscous physiologic fluidmeant for cavity distension;

a fluid supply conduit tube connecting the fluid source reservoir to aninlet port of a variable speed positive displacement inflow pump and anoutlet port of the said inflow pump being connectable to an inflow portof an endoscope instrument through an inflow tube for pumping the fluidat a controlled flow rate into the cavity, the flow rate of the saidinflow pump being termed as the inflow rate;

an inflow pressure transducer being located anywhere in the inflow tubebetween the outlet port of the inflow pump and the inflow port of theendoscope;

an outflow port of the endoscope being connectable to an inlet port of avariable speed positive displacement outflow pump through a outflow tubefor removing the fluid from the cavity at a controlled flow rate, theflow rate of the said outflow pump being termed as the outflow rate,

an outlet port of the outflow pump being connected to a waste fluidcollecting container, and characterized in that a housing tube having acontrollable constriction site is being provided between the fluidsource reservoir and the inflow tube such that the same by-passes theinflow pump; wherein housing tube provides a route for any excess fluidbeing pumped by the inflow pump to bypass the inflow pump and go back tothe fluid supply tube or the fluid source reservoir, thereby minimizingturbulence inside the cavity and maintaining the cavity pressure at astable value despite physiological contractions of the cavity wall.

In an embodiment of the present invention, the fluid source reservoircontaining the non-viscous physiologic fluid is maintained atatmospheric pressure or at a pressure greater than the atmosphericpressure.

In another embodiment of the present invention, a proximal open end ofthe fluid supply tube is connected to the fluid source reservoir and adistal end of the tube is connected to the inlet port of the variablespeed positive displacement inflow pump.

In yet another embodiment of the present invention, the proximal openend of the fluid supply tube is constantly and completely immersed inthe fluid source reservoir.

In still another embodiment of the present invention, a proximal end ofthe inflow tube is connected to the outlet port of the variable speedpositive displacement inflow pump and a distal end of the inflow tubebeing connectable to the inflow port of the endoscope instrument.

In a further embodiment of the present invention, the variable speedpositive displacement inflow pump is selected from the group comprisingperistaltic pump, piston pump, gear pump, diaphragm pump and plungerpump.

In one more embodiment of the present invention, the variable speedpositive displacement inflow pump is a peristaltic pump.

In one another embodiment of the present invention, the housing tube isreleasably provided between the fluid source reservoir and the inflowtube to enable replacement of the housing tube with yet another housingtube having a different diameter at the constriction site to suit theoperational need of the endoscopic procedure.

In a further more embodiment of the present invention, a proximal end ofthe housing tube is connected to the fluid supply tube near its distalend close to the inlet port of the inflow pump.

In an embodiment of the present invention, a proximal end of the housingtube is empties directly into the fluid source reservoir and isconstantly and completely immersed in the fluid source reservoir.

In another embodiment of the present invention, a distal end of thehousing tube is connected to the inflow tube near its proximal end closeto the outlet port of the inflow pump.

In yet another embodiment of the present invention, the housing tube isprovided with a clamping means at the constriction site to enable theuser to vary the diameter of the housing tube at the constriction siteto suit the operational needs of endoscopic procedures.

In still another embodiment of the present invention, the diameter ofthe housing tube at the constriction site is in the range of 0.005 mm toa maximum value which is less than the overall diameter of the rest ofthe housing tube

In one more embodiment of the present invention, the diameter of thehousing tube at the constriction site is in the range of 0.05 to 2.5 mm.

In one another embodiment of the present invention, the inflow pressuretransducer is located sufficiently away from the cavity site, preferablynear the outlet port of the inflow pump from the practical point ofview, such that the actual pressure inside the cavity is measured.

In a further embodiment of the present invention, a proximal end of theoutflow tube being connectable to the outlet port of the endoscopeinstrument and a distal end of the outflow tube is connected to an inletport of the variable speed positive displacement outflow pump.

In an embodiment, the present invention further comprises an outflowpressure transducer connected between the proximal end of the outflowtube and the inlet port of the variable speed positive displacementoutflow pump for measuring the pressure in the outflow tube.

In another embodiment of the present invention, the variable speedpositive displacement outflow pump is selected from the group comprisingperistaltic pump, piston pump, gear pump, diaphragm pump and plungerpump.

In yet another embodiment of the present invention, the variable speedpositive displacement outflow pump is a peristaltic pump.

In still another embodiment of the present invention, the outlet port ofthe variable speed positive displacement outflow pump is connected tothe waste fluid collecting container through a waste fluid carryingtube.

In one more embodiment, the present invention further comprises amicro-controller means electrically coupled to the inflow pressuretransducer, the outflow pressure transducer, the inflow pump and theoutflow pump for regulating the operation of the inflow and the outflowpumps.

In one another embodiment, the present invention further comprises ahousing tube having a variable size constriction site being providedbetween the outflow tube and the waste fluid reservoir.

In another embodiment of the present invention, the fluid supply tube,the inflow tube, the outflow tube and the waste fluid carrying tube areflexible, disposable and are made of polymeric material.

The present invention also provides a method of distending a body tissuecavity of a subject by continuous flow initiation such that minimal ornegligible fluid turbulence is present inside the cavity, such that anydesired cavity pressure can be created and maintained for any desiredoutflow rate, said method comprising the steps of:

-   (a) dispensing a non viscous physiologic fluid meant for cavity    distension from a fluid source reservoir to an inflow port of an    endoscope instrument at a controlled flow rate through a fluid    supply conduit tube, a variable speed positive displacement inflow    pump and an inflow tube, the flow rate of the said inflow pump being    termed as the inflow rate;-   (b) injecting the non-viscous physiologic fluid at a controlled flow    rate into the cavity for distending the body tissue cavity of the    subject;-   (c) removing a waste fluid from the cavity via the outlet port of    the endoscope;-   (d) actively extracting the waste fluid via the outlet port of the    endoscope and transporting it to a waste fluid collecting reservoir    at a controlled flow rate, the said flow rate being termed as the    outflow rate through a outflow conduit tube, a variable speed    positive displacement outflow pump and a waste fluid carrying tube    and-   (e) providing a housing tube having a controllable constriction site    between the fluid source reservoir and the inflow tube such that the    housing tube provides a route for any excess fluid being pumped by    the inflow pump or due the physiologic contraction of the cavity    walls to bypass the inflow pump and go back to the fluid supply tube    or the fluid source reservoir, and also to supply any extra fluid    required as a result of physiologic expansion of the cavity wall,    thereby avoiding turbulence inside the cavity and to maintain a    stable pressure inside the cavity.

The present invention further provides a method of determining theinstantaneous real time rate of fluid intravasation/extravasation duringendoscopic procedures, without using any type of fluid flow rate sensor,said method comprising the steps of:

-   (a) dispensing a non viscous physiologic fluid meant for cavity    distension from a fluid source reservoir to an inflow port of an    endoscope instrument at a controlled flow rate through a fluid    supply conduit tube, a variable speed positive displacement inflow    pump and an inflow tube, the flow rate of the said inflow pump being    termed as the inflow rate “R1”;-   (b) injecting the non-viscous physiologic fluid at the controlled    flow rate into the cavity for distending the body tissue cavity of    the subject;-   (c) removing a waste fluid from the cavity via the outlet port of    the endoscope;-   (d) actively extracting the waste fluid via the outlet port of the    endoscope and transporting it to a waste fluid collecting reservoir    at a controlled flow rate, through a outflow conduit tube, a    variable speed positive displacement outflow pump and a waste fluid    carrying tube wherein the flow rate of the said outflow pump being    termed as the outflow rate “R2”,-   (e) measuring instantaneously the pressure inside the cavity using a    pressure transducer and denoting the determined pressure as “P”, and    obtaining the instantaneous real time rate of intravasation as:    KP=(R1−(R2+R3))    -   wherein K is a constant and R3 is the instantaneous real time        rate of fluid intravasation or extravasation.

The proposed invention is described hereafter with reference to theaccompanying drawings in order to clearly explain and illustrate thesystem and the working of the system. It is respectfully submitted thescope of the invention should not be limited by the description beingprovided hereafter.

The system of the present invention is a unique system for distendingbody tissue cavities in endoscopic procedures. In the proposed inventiona body tissue cavity is distended by continuous flow irrigation in sucha manner that the cavity pressure is absolutely independent of thecavity outflow rate, such the both, the cavity pressure and the outflowrate, may be independently altered without varying the value of theother parameter. The schematic diagram of the invention is shown inFIG. 1. The two peristaltic pumps 5 and 14 operate simultaneously inorder to distend a tissue cavity in such a manner that the cavitypressure is totally independent of the cavity outflow rate. FIG. 1represents the complete schematic diagram of the invention. Please notethat the controller being used in the system shown in FIG. 1 is anoptional feature and the system would provide most of the features evenwithout the controller. The FIG. 2 represents the schematic diagram ofthe invention but without a controller system. Thus FIG. 2 is amechanical version of the invention. A human operator is required tooperate such mechanical version of the invention shown in FIG. 2. Thoughit is recommended that the controller based version of the invention beused in endoscopic surgeries, it is not essential. The controller beingused in the present invention merely assists the user in arriving easilyat some of the additional functions which otherwise can be performedmanually. Thus, in this manuscript the mechanical version of theinvention shown in FIG. 2 is being discussed in more detail in order toexplain the basic physical principals of the invention with a greaterclarity.

Referring to FIG. 2, the system shown in this figure comprises of twoperistaltic pumps which can maintain a predictably precise stable cavitypressure for indefinite time by working simultaneously at constantrotational speeds. Pump 5 pushes fluid into the cavity 18 and while pump14 simultaneously extracts fluid out of the cavity 18. The inlet end ofthe inflow peristaltic pump 5 is connected to a fluid source reservoir 1via tube 2. The distal open end of tube 2 is constantly submerged in asterile non viscous physiological fluid like 0.9% normal saline, 1.5%glycine, ringer lactate or 5% dextrose contained inside the reservoir 1at atmospheric pressure. One end of the tube 7 connects the ‘T junction’3 situated at the inlet end of the pump 5 while the other end of tube 7connects with the ‘square junction’ 6 situated at the outlet end of thepump 5. The ‘T’ junction 3 is thus the meeting point of three tubes,namely 2, 4 and 7. Similarly the square junction 6 is the meeting pointof four tubes, 4, 9, 7 and 10. The rollers of the peristaltic pump 5continuously compress and roll over the entire length of tube 4 thusdisplacing fluid in the direction of the curved arrow. This curved arrowdenotes the direction in which the rotors of the peristaltic pump 5rotate. Tube 7 has a constriction point 8 which can be located anywherealong its length. Such constriction point refers to a point where theinner diameter of the lumen of tube 7 is reduced in comparison to thelumen of the rest of the tube 7. Such constriction may be a permanentconstriction in the lumen of tube 7 or it may be a variable constrictionwhose diameter may be increased or decreased as desired. A pressuretransducer 17 is attached at one of tube 9 while the other end of tube 9is connected anywhere on inflow tube 10. For practical convenience it isdesirable that the said other end of tube 9 be connected in the upstream part of the inflow tube 10 such as at the square junction 6. Thepressure transducer 17 measures the fluid pressure via a column ofliquid or air present in the lumen of tube 9. The fluid pressure asmeasured by the pressure transducer shall be referred to as P. In thismanuscript the term ‘P’ shall frequently be used to refer to the actualpressure inside the tissue cavity but in physical terms P is thepressure sensed by the transducer 17 at point 6. The pressure transducer17 may also be in the form of a membrane diaphragm incorporated in thewall of the inflow tube 10 such that this membrane diaphragm is indirect contact with the fluid contained in the inflow tube 10, such thatthe linear movement excursions of the said membrane are interpreted aspressure of the fluid inside the inflow tube 10 by a suitable pressuretransducer. Such type of pressure sensor being directly incorporated inthe wall of the inflow tube 10 senses the fluid pressure without theintervention of tube 9. The basic purpose of the transducer is tomeasure the fluid pressure inside the inflow tube 10, such as at point6, thus the mechanical construction of the transducer is not importantas long as it measures the fluid pressure. For the sake of simplicitythe existence of tube 9 shall be continued to be considered in the restof the manuscript. The peristaltic pump 14 attached to the outflow sideactively extracts fluid out of the tissue cavity 18 via the out flowtube 12. The outlet end of the pump 14 is connected to a waste fluidcarrying tube 15 which opens into a waste fluid collecting reservoir 16at atmospheric pressure. The rollers of the pump 14 constantly compressand roll over the entire length of the peristaltic pump tubing 13 thusdisplacing fluid in the direction of the curved arrow which alsocorresponds with the direction of pump rotation.

In order to understand the invention in a simpler manner both pumps arebeing considered to be identical in all respects and all the tubes shownin FIG. 6 and the inflow and out flow port are also being considered tobe having the same uniform inner diameter. However the inner diameter ofthe tubes and the inflow and outflow ports can also be different. Theinflow and outflow ports are metallic adaptors located at the proximalend of the endoscope and are meant to connect with the inflow andoutflow tubes respectively, however the said inflow and outflow portshave not been separately shown in any of the figures. Tubes 4 and 13consist of a soft resilient plastic material which can be efficientlycompressed by the rollers of the peristaltic pumps. The other tubes alsoconsist of a suitable resilient plastic material. It is assumed that allthe components shown in FIG. 2, including the two pumps, all tubes andthe said cavity, are placed at the same horizontal height with respectto the ground. Also the rollers of pumps 5 and 14 should pressadequately over tubes 4 and 13 in such a manner that there is no leakthrough these tubes when the pumps are stationary. It is also assumedthat there is no abnormal leak of fluid in the irrigation system, forexample leak via a accidental hole made in any irrigation tube or afluid leak which might occur if the endoscope loosely enters into thetissue cavity, for example in hysteroscopic surgery fluid leaks by thesides of the endoscope if the cervix is over dilated.

One end of the constriction site housing tube 7 instead of beingconnected with tube 2 at the ‘T’ junction 3 can also open directly intothe fluid source reservoir 1. This shall not affect the efficiency ofthe system in any way but it may be practically difficult from thesurgical point of view in some special cases. Thus such a provision isseparately shown in FIG. 9 and the said tube has been labeled as 11 butit has intentionally not been included in the main block diagram of theinvention as in FIGS. 1 and 2 in order to keep the drawings simple. Alsoa constriction site housing tube similar to tube 7 labeled as 17 can beattached to the outflow tube 12 as shown in FIG. 9. In the said tube 17the said constriction site is labeled as 19. Such tube can serve anumber of purposes. Tube 17 can be utilized for relatively fasterevacuation of air bubbles from the cavity. The said bubbles areinvariably created inside the cavity as a result of electrosurgicalcutting and coagulation or they may enter the cavity while the endoscopeis being introduced into the cavity. Such bubbles cause extreme nuisancefor the surgeon because they obscure vision and thus the surgical timemay be greatly increased. In routine surgery the surgeon moves the tipof the resectoscope near the bubble and the bubble is sucked out of thecavity by the process of continuous flow irrigation. However in certainsituations it may not be possible to bring the tip of the resectoscopenear the bubble, one such situation is when bubbles accumulate inside avery deep cornuae associated with a long septum, the diameter of thecornuae being less than the outer diameter of the resectoscope. In sucha situation the tubal opening situated at the center of the cornuae canonly be visualized after evacuating such bubbles from the cavity. Insuch situation the bubbles can be quickly evacuated without moving thetip of the resectoscope near the bubbles by simply opening theconstriction 19 in the tube 17. However such maneuver tends tocompletely collapse the cavity. Thus if the resctoscope tip is onlymoderately away from the bubbles the constriction is opened onlypartially so that the bubbles are sucked out and the cavity collapses bya relatively smaller magnitude. In place of the adjustable constrictionsite 19 a pressure release safety valve may be incorporated as a safetyfeature, however it is more beneficial to install such pressure safetyvalve in the inflow circuit. The tube 17 may also be used for quicklyflushing air bubbles from the irrigation tubes by fully opening theconstriction site 19 for a few minutes or seconds. The tube 17 may alsobe used for any other purpose as deemed fit by the surgeon. However thesaid tube 17 has intentionally not been included in the main blockdiagrams of the invention because by including the tube 17 in the mainblock diagrams it would have become very difficult to explain the basicphysical principals of the invention. However tube 17 is a verybeneficial component and is thus recommended to be incorporated in thesystem of the proposed invention. The opening and closing of theconstriction site 19 can also be regulated manually to help in variousspecial advanced endoscopic applications. Incorporation of tube 17 withthe variable constriction site 19 can help in reducing the substantiallyhigh amplitude pressure variations inside the cavity caused byabnormally large cavity wall contractions, but such phenomenon is onlyrarely encountered. Also an additional pressure transducer 18 may alsobe attached on the out flow tube 12, if desired, as shown in FIG. 9.However the said pressure transducer 18 has intentionally not beenincluded in the main block diagrams of the invention because by doing soit would have become very difficult to explain the basic physicalprincipals of the invention.

In order to clearly understand the system shown in FIG. 2 it would behelpful to discuss the functioning of the inflow peristaltic pump 5 as aseparate entity as shown in FIG. 3. The rollers of pump 5 move in thedirection of the curved arrow and squeeze over the entire length ofperistaltic pump tubing 4. Initially tubes 2, 4, 7 and 9 contain air atatmospheric pressure and the free open end of tube 2 is submerged in asterile fluid contained inside the fluid source reservoir 1. The momentthe constriction site 8 is fully occluded a column of fluid isimmediately sucked into tube 4 via tube 2, and thus fluid startsaccumulating in the proximal parts of tubes 9 and 7. As the fluid fillsin tube 9 it pushes a column of air distal to the fluid column createdin tube 9 and the pressure of this compressed air column is sensed bythe pressure transducer 17. The fluid pressure and the pressure of thesaid compressed air column are same thus the pressure transducer 17actually senses the fluid pressure. If tube 7 continues to remain fullyoccluded at the constriction site 8, the fluid continues to accumulateinside tubes 9 and in that part of tube 7 which lies between point 6 andthe constriction site 8, and the pressure transducer 17 thus displays acontinuously rising fluid pressure. The moment the block at theconstriction site 8 is partially released the fluid escapes in the formof a jet through the partially open constriction opening 8 in thedirection of point 3. With the constriction opening 8 being onlypartially blocked, if the pump 5 continues to rotate at a constantrotational speed the fluid pressure ultimately gets stabilized at afixed value provided the internal diameter of the constriction site 8 isnot further varied. The diameter D of the constriction site 8 rangesfrom a minimum non-zero value to a maximum value which is less than theoverall diameter of the rest of the housing tube, that is when theconstriction site 8 is fully occluded, to a maximum value which is equalto the diameter of tube 7. Henceforth in this manuscript the innerdiameter of the constriction site 8 shall be deemed to be fixed at somepredetermined value D, unless otherwise stated. The fluid beingdisplaced by the peristaltic pumps is actually pulsatile in nature thusthe fluid pressure exhibits minute pulsations having a fixed frequencyand a fixed amplitude. From the practical point of view such minutepressure fluctuations of such a regular nature can be ignored in contextwith distension of body tissue cavities in endoscopic procedures.Henceforth in the entire manuscript the fluid pressure shall be assumedto be non-fluctuating in nature.

Referring to FIG. 4, this figure is similar to FIG. 2 but a limitedregion of the irrigation circuit having an almost same pressure has beenshaded black. Due to frictional resistance experienced by the movingfluid the pressure at point 6, as sensed by the transducer 17, is alwaysfound to be higher than the actual pressure inside the tissue cavity 18but the said pressure difference is so small that it may be neglectedfrom the practical surgical point of view. Also such pressure differenceincreases as the fluid flow rate increases. In a simulated experimentalendoscopic model, as explained hereafter, such pressure difference wasfound to be only 2 mm Hg at a out flow rate of 500 ml/minute, while atoutflow rates less than 400 ml/minute this pressure difference was sosmall that it had not been possible to demonstrate it experimentally.The term ‘out flow rate’ being referred to the flow rate of pump 14.Also, the said pressure difference remains constant all through surgeryat any fixed outflow rate. Though the said pressure difference isnegligible but if desired its effect can also be totally negated bysubtracting its value from the pressure reading of the transducer. Inthis manner, in endoscopic surgeries, it is possible to determine theactual cavity pressure by using the pressure transducer 17 located faraway from the cavity. This feature is of special relevance because inendoscopic procedures like hysteroscopy, arthroscopy and brainendoscopic surgery while it is important to know the actual cavitypressure but at the same time it is practically difficult to take apressure measurement directly from the cavity. The physical principalsrelating to this have been discussed in detail below.

Referring to FIG. 2 it shall be first described as to how the system ofthe proposed invention can be used mechanically, that is without acontroller. The peristaltic pumps 5 and 14 can be made to work at anyfixed rotational speed and the fluid flow rate of each pump is directlyproportional to the pump RPM or the pump rotational speed. Thus anyprecise pump flow rate can be generated by selecting a suitable pumprotational speed. The fluid flow rate of pump 14 shall henceforth bedenoted by R2 and shall be termed as the ‘outflow rate’. The fluid flowrate of pump 5 shall be denoted by R1 and shall be termed as the ‘inflowrate’ Here it is to be noted that the term ‘inflow rate’ R1 is not thetrue inflow rate for the cavity 18, as might be suggested by theliterary meaning of the term ‘inflow’ because R1 is not the actual rateat which fluid into the cavity 18 because some fluid also constantlyescapes through the constriction site opening 8. Henceforth in theentire manuscript the term ‘inflow rate’ shall only be referred to theflow rate of the inflow pump 5 unless specifically mentioned. Howeverthe term ‘outflow rate’ R2 does correspond to the literary meaning ofthe term ‘outflow’ because R2 is equal to the rate at which fluid flowsout of the cavity 18. The surgeon initially decides an out flow rate R2by selecting a suitable rotational speed for pump 14. Next the surgeondecides the maximum flow rate at which fluid could be allowed to enterinto the cavity via the inflow tube 10 and the inflow pump 5 is set towork at such flow rate or at a flow rate slightly lesser than this. Asdiscussed in paragraph 26, intravasation is process by which fluidenters into the patient's blood circulation through the cut ends ofblood vessels located in the cavity wall or enters into the patient'sbody, for example into the peritoneal cavity, as a result of anaccidental perforation or escapes via patent fallopian tubes into theperitoneal cavity. Thus ‘intravasation’ is a process by which thepressurized irrigation fluid enters into the patient's body systemthrough the walls of the tissue cavity. In case of a surgical accidentlike cavity wall perforation the fluid being pumped by the inflow pump 5can enter into the patient's body at a rate almost equal to R1. It isobvious that the maximum rate of fluid intravasation cannot exceed thevalue R1. In case of an accident like cavity wall perforation it maytake some time before an abnormally high intravasation rate isdiscovered and in such time a dangerous quantity of fluid might enterinto the patient's body. If the inflow rate R1 is kept at a relativelylower value then the volume of intravasated fluid in case of such anaccident would be low. After fixing the values for R2 and R1 the systemis started and the diameter of the constriction site 8 is graduallyreduced. As the diameter of the constriction site 8 is reduced fluidstarts flowing into the tissue cavity and the pressure inside the tissuecavity starts rising. When the desired pressure is achieved inside thetissue cavity the diameter of the constriction site 8 is not reduced anyfurther and is fixed. The diameter of the constrictions site at thisstage is termed as “D”. The constriction site may also be a plastic ormetal piece which has a hole in the centre such that the diameter of thehole is permanently fixed at some value D. If a constriction 8 has apermanently fixed diameter then only the flow rates of pumps 14 and 5have to be set before the system becomes completely operational.

The Inventors here would like to discuss about the importance ofincorporating the housing tube 7 with the constriction site and thenon-obvious advantages provided by the housing tube 7 with theconstriction site.

As mentioned earlier, till date the surgeons were left with only twooptions, either to ignore the said cavity pressure variations by notcorrecting them, or to externally and actively correct such pressurevariations. To externally and actively correct the variations in thecavity pressure, controller was incorporated and the working of thepumps were essentially controlled by the controller. Incorporation ofthe controller controlling the operation of the pumps did not provideany benefit. The controllers used to activate the controlling actionafter the variations in the cavity pressure had subdued. Thus, thecontrolling action initiated by the controller instead of benefiting thesurgeon leads to an undesirable turbulence inside the cavity and alsotends to amplify the resultant movement excursions of the cavity walls.

The Inventors have noticed that if the controller continuously controlsthe operations of the pumps (either on the inflow side or on the outflowside), the cavity pressure continuously fluctuates around a preset valueand it not at all possible to attain a constant value. The Inventorsbelieve that the controller provides proper corrective action (bycontinuously controlling the operations of the pumps) only if thefluctuations in the cavity pressure are gradual and not highlyinstantaneous. That is, if the quantitative rise/fall in the cavitypressure is over long time period, the controller would be able toprovide proper corrective action. As the time period to detect variationin the cavity pressure and commence corrective action is ideally in therange of 2 to 4 seconds, if the quantitative rise/fall in the cavitypressure is over very short time period, the suggested mechanism ofproviding a controller will be unsuitable. Under such instances, insteadof providing any corrective action, the controller destabilizes thesystem and induces additional pressure fluctuations inside the cavity(because of commencing a corrective action at a delayed stage). Thus ittakes very long time period for the system to once again get stabilized.

The Inventors have surprisingly found that by incorporating a housingtube provided with a constriction site at the inflow side as describedabove, inherently and passively corrects the pressure variations due tophysiological cavity wall contractions and the mechanical movement ofthe tubes and the endoscope and also limits the variation in the size ofthe cavity. The Applicants would like to highlight that it is importantto control both the variations in the pressure inside the cavity and thechanges in the size of the distended cavity. Large variations in thepressure inside the cavity or the size of the cavity are detrimental tothe surgical procedure. In all the prior art systems attempts were madeto either control the variations in the pressure or the variations inthe cavity size. But none of the prior art document the need to controlboth the cavity pressure variations and the cavity size variations andhence failed to provide a safe and ideal system. During the contractionof the cavity, a minute quantity of the fluid is pushed out of thecavity. If during this stage the system does not provide a way forreleasing the fluid being pushed out, the instantaneous pressure insidethe cavity increases tremendously which is harmful to the patient. Onthe other hand, if the amount of fluid being pushed out of the cavity isnot checked/controlled, the changes in the size of the distended cavityare very high. The incorporation of the housing tube having theconstriction site for the first time in the present system controls boththe variations in the pressure inside the cavity and the changes in thesize of the distended cavity The housing tube having the constrictionssite provides a by-pass route for the fluid being pushed out of thecavity to go back to the fluid supply tube or the fluid sourcereservoir. This avoids the instantaneous pressure surge inside thecavity which is harmful to the patient. The size of the diameter at theconstrictions automatically controls the amount of fluid passing throughthe housing tube, thereby controlling the amount of fluid being pushedout of the cavity. Inclusion of the housing tube with the constrictionssite therefore minimizes the instantaneous variations in the size of thedistended cavity.

Alternatively if the cavity expands a suitable volume of fluid is suckedinto the cavity from the irrigation circuit, such as from the region ofpoint 6, and this is accompanied by a corresponding transient decreasein the flow rate at which fluid which fluid is escaping via theconstriction site 8 in the direction of point 3 but if the magnitude ofthe said physiological expansion is more fluid may even be sucked intothe cavity via the constriction site 8. This implies that theconstriction site 8 is helping in maintaining a stable cavity pressuredespite physiological cavity wall contractions by suitably varying themagnitude of an imaginary fluid flow vector passing through theconstriction site 8.

Determining the Real Time Rate of Fluid Intravasation:

Again referring to FIG. 2, let it be hypothetically assumed that thediameter at the constriction site 8 has been fixed at some predeterminedvalue D, the outflow and the inflow rates have been fixed at some valuesR2 and R1 respectively and in such a situation a pressure P is createdinside the tissue cavity 18 when the system is operated. In such a caseif no intravasation occurs during the endoscopic procedure then thepressure inside the tissue cavity 18 continues to remain at the samevalue P. However, if at any stage during the endoscopic procedureintravasation occurs then the cavity pressure immediately falls belowthe desired initial value P and inflow rate has to be increased by somemagnitude in order to raise the cavity pressure to its initial value P.Here magnitude of the required increase in the inflow rate to attain theinitial cavity pressure P is equal to the instantaneous real time rateof intravasation R3 existing at that moment of time. In this way thereal time rate of fluid intravasation can be determined by using themechanical version of the proposed invention.

Cavity Pressure or the Outflow Rate, Both Can be Altered Independentlywithout Varying the Value of the Other Parameter:

Referring again to FIG. 2 an hypothetical endoscopic procedure is beingconsidered where surgery is being performed at an outflow rate R2 andinflow rate R1 with the constriction 8 diameter being been fixed at somevalue D and a resultant cavity pressure P being created maintained. Insuch hypothetical situation as long as R2 and R1 are not altered thecavity pressure P remains predictably constant throughout surgeryresulting in a predictably stable mechanical distension of the tissuecavity walls which culminates in constant clear visualization throughoutthe endoscopic procedure. If in the said hypothetical procedure thecavity pressure needs to be increased without altering the out flow rateR2 then all that is needed is to start increasing the value of R1 andstop doing so when the desired higher cavity pressure is achieved.Similarly if the cavity pressure needs to be decreased without alteringthe out flow rate R2 then R1 is decreased till the desired lower cavitypressure is attained. In the said hypothetical endoscopic procedure ifthe outflow rate R2 needs to be increased without altering the cavitypressure P then the value of R2 is increased by the desired magnitudebut simultaneously the value of R1 is also increased by a similarmagnitude. Similarly, if the outflow rate R2 needs to be decreasedwithout altering the cavity pressure P then the value of R2 is decreasedby the desired magnitude but simultaneously the value of R1 is alsodecreased by a similar magnitude. Thus if R1 and R2 are simultaneouslyincreased or decreased by the same magnitude the cavity pressure doesnot vary, the value D is always fixed as already stated. The precedingstatements shall now be explained by the help of a numericalhypothetical example. In reference to FIG. 2 considering a hypotheticalsituation in which an endoscopic procedure is being done at an outflowrate of 100 ml/minute, an inflow rate R1 and the cavity pressure being80 mm Hg. If the surgeon wants to increase the outflow rate to 322ml/minute by maintaining the cavity pressure at the same value of 80 mmHg outflow rate is increased to 322 ml/minute and the inflow rate isincreased by 222 ml/minute, because 322 ml/min-100 ml/min=222 ml/minute.As already mentioned in this paragraph if both inflow and outflow ratesare increased or decreased by the same magnitude the cavity pressuredoes not change. Thus the final inflow rate becomes R1+222 ml/minute,where R1 was the initial inflow rate. Thus in the proposed invention thecavity pressure and the outflow rate both can be altered absolutelyindependent of each other without affecting the value of the otherparameter.

Mechanical Version of the Invention:

The mechanical version of the invention shown in FIG. 2 can be usedpractically in endoscopic surgeries but it requires a skilled operatorhaving a detailed knowledge of the physical principals involved incavity distension, which may not be always possible. Also the mechanicalversion has certain practical limitations which shall be explained inthe later sections of the manuscript. This mechanical version of theinvention has been discussed only in order to explain more clearly thephysical principals associated with the controller based version of theinvention shown in FIG. 1.

Controller Based Version of the Invention:

Referring to FIG. 1, this figure shows a schematic diagram of the maininvention which is proposed to be used in endoscopic procedures. FIG. 1and FIG. 2 are similar except that in figure except that in FIG. 2 thecontroller system is not included. A tachometer, not shown in thediagrams, is coupled to each peristaltic pump and sends informationregarding the pump rotation speed to the controller 19 via wires 20 and23. The pump flow rates being proportional to the pump rotation speedthe tachometer signal always conveys flow rate related information tothe controller. As already mentioned in paragraph 51 both peristalticpumps have been considered to be similar in all respects because thismakes it easier to understand and operate the system. However the twoperistaltic pumps may also be different in context with the innerdiameter of the peristaltic pump tubes 4 and 13 but in such casesuitable modifications have to be made in the controller programming inorder to operate the system as described in this manuscript. Thecontroller also regulates the rotation speed of the two pumps viaelectrical signals sent through wires 24 and 21. The pressure transducer17 conveys the pressure signal to the controller via wires 22. On thebasis of a pressure feed back signal received from the pressuretransducer 17 the controller regulates the rotational speed of theinflow pump 5. The outflow pump 14 works at fixed outflow rates and theflow rate of this pump is also regulated by the controller via suitableelectrical signals sent via wires 21. A provision exists by whichdesired values for P and R2 can be fed into the controller and thevalues R1, R2 and P can be continuously displayed via suitable displaymeans incorporated in the controller. The controller can be programmedto perform many special functions related to endoscopic surgery whichshall be discussed in the following paragraphs.

Method of Operating the Controller Based Version of the Invention:

Again referring to FIG. 1, in context with the present invention at thestart of surgery the surgeon initially selects suitable values forcavity pressure P and outflow rate R2. The said desired values of P andR2 are fed into the controller via suitable input means incorporated inthe controller. The diameter D at the constriction site 8 remains fixedat some pre selected value. The diameter of the constriction site 8 isso chosen that it suits the operational needs of the endoscopicprocedure. The method of selecting a suitable diameter D for theconstriction site 8 has already been discussed under the heading‘Selection of a suitable diameter for the constriction site’. When thesystem shown in FIG. 1 is operated the controller 19 instructs theoutflow pump 14 via wires 21 to continuously extract fluid out of thebody cavity 18 at a desired fixed outflow rate R2. Thus all through thesurgery the outflow rate remains fixed at R2 irrespective of anyinternal or external factors unless intentionally changed by thesurgeon. The cavity pressure is sensed by the pressure transducer 17 anda corresponding pressure feedback signal is sent to the controller viawires 22 on the basis of which the controller regulates the inflow rateR1, via wires 24. After the system is made operational the controller 19gradually increases the inflow rate up to the point where the desiredpreset cavity pressure P is achieved. Let the value of the inflow rateat which the desired cavity pressure is achieved be termed as‘R1.Final’. It is obvious that the value ‘R1.final’ is actuallydetermined by the controller by a pressure feed back mechanism and suchdetermination of the value ‘R1.Final’ is based on the preset values ofR2 and P. The controller is so programmed that once the value ‘R1.Final’is achieved and is maintained for a desired minimum time interval, forexample 10 seconds, after which the controller releases the inflow pump4 from its pressure feedback control mechanism and allow the inflow pump4 to operate on its own at an inflow rate ‘R1.Final’ which wasdetermined by the controller. In this manner the two peristaltic pumpscontinue to work at fixed flow rates to maintain a desired stable cavitypressure. The controller is also programmed that in case the cavitypressure subsequently alters, for example due to intravasation, by adesired minimum preset magnitude and for a desired minimum time, whichmay hypothetically be 10 seconds, the inflow pump 4 again comes underthe pressure feedback control of the controller and a new value of‘R1.Final’ is determined by the controller after which the inflow pump 4is again allowed to be operated without the pressure feedback mechanismat the newly determined ‘R1.Final’ inflow rate. Such sequence of eventscontinue to occur throughout the endoscopic procedure. Taking animaginary example if the total surgical time is 60 minutes then it maybe hypothetically possible to operate the inflow pump independent of thepressure feedback mechanism for 55 minutes and under the control of thepressure feedback mechanism for 5 minutes. However, provision ofoperating the inflow pump 4 under a pressure feedback mechanism allthrough the endoscopic procedure can also be incorporated.

The Advantage of Operating the Inflow Pump Independent of The PressureFeedback Mechanism:

The only reason for operating the inflow pump 4 independent of thepressure feedback mechanism is to avoid unnecessary corrections of minorpressure variations caused by physiological cavity wall contractions.The concept of physiological cavity wall contractions has been explainedin detail under the heading ‘basic physics of cavity distension’. In thepresent invention the physiological variations in cavity pressure areautomatically corrected by the constriction site 8 without the need of acontroller. If the cavity contracts a minute quantity of fluid which ispushed out of the cavity escapes via the constriction site 8 towardspoint 3. It is to be noted that the part of tube 7 between point 8 and 3is at atmospheric pressure thus the fluid which is expelled from thecavity as a result of a physiological contraction escapes through theconstriction site 8 against a zero pressure head, which is atatmospheric pressure. Thus, the transient, insignificant andinstantaneous rise/fall in cavity pressure variations get stabilized atthe desired preset value within a fraction of seconds. Alternatively ifthe cavity expands a suitable volume of fluid is sucked into the cavityfrom the irrigation circuit, such as from the region of point 6, andthis is accompanied by a corresponding transient decrease in the flowrate at which fluid which fluid is escaping via the constriction site 8in the direction of point 3 but if the magnitude of the saidphysiological expansion is more fluid may even be sucked into the cavityvia the constriction site 8. This implies that the constriction site 8is helping in maintaining a stable cavity pressure despite physiologicalcavity wall contractions by suitably varying the magnitude of animaginary fluid flow vector passing through the constriction site 8.Normally the direction of such imaginary vector is always towards point6 while its magnitude constantly varies to take care of the pressurechanges resulting due to physiological cavity contractions. Normally acavity continuously contracts and dilates by approximately the samemagnitudes thus there is no logic to check the minor pressure variationsemanating from the said contractions. Also the opening of theconstriction site 8 does not allow the said physiological cavitypressure fluctuations to cause any significant cavity wall movementexcursions by allowing to and fro movement of flow through its lumen.However, if the said pressure changes are made to be corrected by acontroller, as is done in the prior art systems, the cavity wall mayexhibit significant irregular pressure fluctuations which may result insignificant movement excursions of the cavity wall, thus disallowing apredictably stable mechanical stabilization of the cavity walls.However, in the eventuality of fluid intravasation the fall in cavitypressure drop is relatively more permanent in nature thus needs to becorrected by the controller. As explained in the previous paragraph thecontroller is so programmed that the inflow pump 4 automatically comesunder the pressure feedback control mechanism of the controller in casethe cavity pressure alters by a desired minimum preset magnitude and fora desired preset time interval, thus a new ‘R1.Final’ inflow rate isestablished at which the inflow pump is again allowed to operate withoutthe feedback control of the controller. As a safety precaution aprovision can be made in the controller via suitable input means to fixan upper safe limit for the inflow rate R1 and the cavity pressure Psuch that these safe limits are riot exceeded accidentally.

Controller Programming for Determining the Instantaneous Rate of FluidIntravasation During Surgery

In the above paragraphs a mechanical method of determining theinstantaneous real time instantaneous rate of fluid intravasationwithout using the controller has been described. However such mechanicalevaluation is subject to human error and is also difficult to repeatmultiple times during an endoscopic procedure. Hence, the need arises tocontinuously determine and display the real time rate of fluidintravasation by the help of the controller. Excess fluid intravasationduring an endoscopic procedure can even lead to the patient's death thusit is extremely important for the surgeon to reliably, accurately andconstantly know the real time rate of fluid intravasation R3 throughoutthe endoscopic procedure. In order to determine the real time rate ofintravasation an equation KP=(R1−(R2+R3))² has been derived whereK=constant, P=cavity pressure, R1=inflow rate, R2=outflow rate andR3=instantaneous rate of fluid intravasation. Let this equation bereferred to as equation 1. In equation 1, the values of P, R1 and R2 arealways known by the controller and the value of the constant K can bedetermined by suitable analytical means. Thus in equation 1, R3 is theonly unknown value which can be determined by feeding the expressioncontained in the equation 1 into the controller via suitable programmingmeans and directing the controller to continuously determine and displayR3. The controller can be further programmed to carry out multiple otherfunctions related to intravasation such as an alarm being sounded ifintravasation of a specific minimum magnitude occurs or if the rate ofintravasation rate increases by a specific magnitude. The controller canalso be programmed to completely shut down the system in case the rateof intravasation exceeds a specified dangerously high rate. The equation1 has been derived experimentally, and the said experimental methods aredescribed in the subsequent paragraphs.

Experimental Determination of Equation 1

The equation 1 has been determined by using an experimental setup asshown in FIG. 3. In FIG. 3 the inflow tube 10, the cavity 18, theoutflow pump 14, the tube 15 and the waste fluid collecting vessel 16are not included otherwise FIG. 3 is similar to FIG. 2. The peristalticpump shown in the experimental set up shown in FIG. 3 was operated byincreasing the inflow rate R1 and the corresponding values of R1 and Pwere plotted on a graph paper. The values R1 were plotted on the X axiswhile the corresponding values of P were plotted on the Y axis and thesaid plotted values are represented by small dots in FIG. 5. By the helpof a suitable computer programme a curve corresponding to each set ofdots was created and superimposed over the said dots. In this mannerthree curves 1, 2 and 3, were experimentally plotted and are shown inFIG. 5. All of the said dots do not fall exactly over the resultantcurve because of mechanical errors and variations associated withpractical experimentation. The values of R1 are in ‘ml/minute’ andcorrespond to the X axis, while the values of P are in ‘mm Hg’ andcorrespond to the Y axis. In order to plot curve 1 the constriction site8 was substituted by a 20 guage hypodermic injection needle which isused for giving injections to the patients and the experiment asdescribed above was conducted. The curve 2 and 3 were similarly drawn bysubstituting the constriction site 8 as shown in FIG. 3 by 18 guage and16 guage hypodermic injection needles respectively. The inner diameterof a 16 guage needle is more than the inner diameter of an 18 guageneedle which in turn is more than the inner diameter of a 20 guageneedle. The experimental values related to each of the three curves aredepicted in table 11 which is as follows: TABLE 11 Data for curves 1, 2and 3: Curve 1 Curve 2 Curve 3 (Drawn by using (Drawn by (Drawn by 20guage using 18 Guage using 16 Guage hypodermic hypodermic hypodermicinjection needle) injection needle) injection needle) R1 P R1 P R1 P(ml/min) (mmHg) (ml/min) (mmHg) (ml/min) (mmHg) 8 2 16 2 22 2 12 6 20 633 6 21 16 32 14 68 20 30 32 42 24 88 28 42 58 54 34 105 35 64 112 62 44120 44 74 144 74 56 152 64 86 184 84 68 168 74 96 248 96 82 190 86 100280 105 96 208 98 112 108 223 110 124 128 234 120 130 142 254 140 142164 270 156 153 190 285 172 163 218 298 186 168 244 310 198 180 282 320210 335 224 345 238 355 250 365 266 380 290

The curves 1, 2 and 3 appear to be parabolas and the mathematicalexpression for a parabolic curve being X²=CY, where X is a variablerelated to the X axis, C is a constant and Y is a value related to the Yaxis. In order to confirm the parabolic nature of curves 1, 2 and 3 thenumerical values related to these three curves were again considered butthis time curves were plotted by taking the square values of R1 on the Xaxis and the values P over the Y axis and the resultant curves 4, 5 and6 as shown in FIG. 6 are straight line curves cutting the X and the Yaxis at zero point. Such mathematical exercise proves the curves 1, 2and 3 to be parabolas. By substituting R1 and P in the said parabolicexpression X²=CY an equation 2 is derived which is (R1)²=KP where K is aconstant. The numerical values (R1)² and P taken for plotting curves 4,5 and 6 are depicted in table 12 which is as follows. TABLE 12 Data forcurves 4, 5 and 6: Curve 4 Curve 5 Curve 6 (R1)² P (R1)² P (R1)² P 64 2256 2 484 2 144 6 400 6 1089 6 441 16 1024 14 4624 20 900 32 1764 247744 28 1664 58 2916 34 11025 35 4096 112 3844 44 14400 44 5476 144 547656 23104 64 7396 184 7056 68 28224 74 9216 248 9216 82 36100 86 10000280 11025 96 43264 98 12544 108 49729 110 15376 128 54756 120 16900 14264516 140 20164 164 72900 156 23409 190 81225 172 26569 218 88804 18628224 244 96100 198 32400 282 102400 210 112225 224 119025 238 126025250 133225 266 144400 290Substituting ‘R1’ BY ‘(R1−(R2+R3))’:

Referring to the equation 2, that is KP=(R1)², in physical terms R1 isthe rate at which fluid fills into tubes 7 and 9 as shown in FIG. 3. Butin context with FIG. 2, the rate at which fluid fills into tubes 7 and 9is equal to (R1−(R2+R3)) because the outflow R2 and the intravasation R3are two processes which constantly remove fluid from tubes 7 and 9 at arate R2+R3 while the pump 5 pushes fluid into these tubes at a rate R1.Thus the net rate at which fluid tends to accumulate in the irrigationcircuit comprising of the inflow tube 10, the cavity 18 and the outflowtube 12 is equal to (R1−(R2+R3)). In context with FIG. 3 it is extremelyimportant to understand that in actual physical terms R1 is the rate atwhich fluid tends to accumulate in the irrigation circuit comprising ofthe tube 9 and that part of tube 7 which lies between point 6 and theconstriction point 8. Thus, in context with FIG. 2 the value R1 can besubstituted by the value (R1−(R2+R3)). By substituting the value(R1−(R2+R3)) in place of the value R1 in equation 2 the originallyproposed main equation 1 is derived, which being KP=(R1−(R2+R3))₂.

A Less Accurate Method of Determining the Instantaneous Rate of FluidIntravasation:

As described in the preceding paragraphs the real time instantaneousrate of fluid intravasation R3 can be accurately determined by usingequation 1 and such method is not handicapped by any flow rate orpressure limits. R3 can be determined in a different way also but thismethod is an inferior and less accurate way of determining R3 and isbeing mentioned more from the academic point of view and may notnecessarily be used in actual practice. In the said less accurate methodan equation P=(K1×(R1−(R2+R3))+K2 is used for calculating the value R3and such equation is being labeled as equation A. In equation A, P isthe cavity pressure, K1 is a first constant, R1 is the inflow rate, R2is the out flow rate, R3 is the real time rate of intravasation and K2is the second constant. Equation A is a linear expression and can beused for determine R3 within a specific range for cavity pressure andflow rate. In the system shown in FIG. 1 information regarding P, R1 andR2 is constantly available to the controller 19 via wires 22, 23 and 20respectively. In equation A, R3 is the only unknown value which needs tobe determined. On the basis of the linear expression contained theequation A the controller 19 can be programmed to constantly determineand display the value R3. This less accurate method of determining theinstantaneous real time rate of fluid intravasation by using theequation P=(K1×(R−(R2+R3))+K2 is also being proposed because such methodcan facilitate the determination of the real rate of fluid intravasationin the mechanical version of the invention. For financial reasonscertain hospitals, especially in developing countries, may be able toafford the mechanical version of the proposed invention. In the priorart systems there is no provision of determining the real time rate offluid intravasation in the manner described in this manuscript.

Experimental Determination of Equation A:

The curves 1, 2 and 3 shown in FIG. 5 have already been derived using anexperimental setup as shown in FIG. 3 and the related experimental stepsare described under the heading ‘Experimental determination of equation1’. Referring again to FIG. 5, on close inspection it is seen that acentral part of each of the three curves resembles an almost straightline. All three curves can help in the determination of R3, however thecurve 3 appears most appropriate for this purpose. Upon carefulexamination of curve 3 it is seen that a part of this curve lyingbetween the values 70 ml/min to 300 ml/min for R1 and 20 mmHg to 190 mmHg for P appears almost linear thus for all practical purposes suchcentral part of the parabolic curve 3 may be considered to be an almoststraight line. The values of R1 between 70 ml/min to 300 ml/min and thevalues of P between 20 mmHg to 190 mm Hg related to curve 3 were plottedseparately and an approximate linear approximation for all these valueswas determined and the same has been labeled as curve 7 as shown in FIG.7. This straight line curve 7 can be used for determining R3 in anapproximate and less accurate manner.

The part of the straight line curve 7 which can be used for determiningthe real time rate of fluid intravasation in endoscopic surgeriesappears to lie between R1=70 to 300 ml/min and P=10 to 170 mm Hg. Curve7 when extrapolated towards the Y axis cuts the Y axis towards its minusside at a value K2 which being the value of the second constant inequation A. The mathematical expression for curve 7 can be written inthe form of equation B which is P=(K1×R1)+K2 where P=pressure measuredby the transducer 17, R1=Flow rate of pump 5, K1 is a first constant andK2 is the second constant having a negative value corresponding to thepoint where the extrapolated part of curve 7 cuts the Y axis. As alreadyexplained in paragraph 64 value ‘(R1−(R2+R3))’ can be substituted inplace of the value R1. Thus by substituting the value (R1−(R2+R3)) inplace of the value R1 in equation B, the original equation A initiallyproposed in paragraph 65 is derived, the equation beingP=(K1×(R1−(R2+R3))+K2.

Selection of a Suitable Diameter for the Constriction Site:

The three curves drawn in FIG. 5 are not similar because whiledetermining these three curves constriction sites of three differentdiameters D were used in the experiment. This implies that the shape ofsuch curves is influenced by the value D. Referring to FIG. 5, curve 1appears unsuitable for endoscopic surgeries because the curve rises verysteeply with minimal increase in the inflow rate R1. Curve 3 is veryflat and appears relatively more suitable for endoscopic surgeries likehysteroscopy, arthroscopy, transuretheral surgery and other endoscopicsurgeries utilizing continuous flow irrigation because in curve 3 asteep rise in the pressure P is not seen even with a substantialincrease in the inflow rate R1. As already stated under the heading‘Experimental determination of equation 1’, in order to plot curves 1, 2and 3 the constriction site 8 had been randomly substituted by a 20, 18and 16 guage by hypodermic injection needles respectively. The diameterof 20 guage needle being is less than the diameter of an 18 gauge needlewhich is less than the diameter of a 16 guage needle. It is observedthat any reduction in the value of D tends to tilt the curve towards theY axis and while any increase in the value D tends to tilt the curvetowards the X axis as shown in FIG. 5. The 20, 18 and 16 gauge needleshave been selected at random and there is no specific reason for havingselected needles of these particular diameters only, so the selection ofguage for the said system should not construed to limit the scope ofinvention. More such curves can be plotted by increasing theconstriction site diameter more than the diameter of a 16 guage needleand the most suitable such curve which fulfills the operational needs ofan endoscopic procedure or procedures can be experimentally derived andthe constriction site diameter D found associated with the most suitablecurve can be permanently substituted in place of the constriction site8. In this manner the most suitable diameter D for the constriction site8 can be selected for endoscopic procedure or procedures but such anapproach does not take into consideration the operational efficiencyneeds in context with the cavity pressure fluctuations which might occurdue to the inevitable physiological contraction or expansion of thecavity walls. If the diameter of the constriction site 8 is very smallthen the said transient pressure fluctuation in the cavity pressurewould be of a relatively larger magnitude and would last for arelatively longer time interval but the associated resultant movementexcursion of the cavity wall would be of a relatively small amplitude.Similarly if the diameter of the constriction site 8 is very large thenthe said transient cavity pressure fluctuations would be of a relativelysmaller magnitude and would last for a relatively shorter time intervalbut the associated resultant movement excursion of the cavity wallswould be of a much larger amplitude. These statements are explained bythe help of three hypothetical numerical assumptions as stated in table13 which is as follows: TABLE 13 A hypothetically assumed numericalvalue of the magnitude of a transient pressure surge associated Ahypothetically assumed A hypothetically assumed A hypothetically assumedwith a physiological time interval for which magnitude of the Serialnumber of the numerical value of the cavity wall contraction the saidpressure surge associated resultant cavity assumption constriction sitediameter movement exists wall movement excursion 1 0.1 mm 20 mm Hg    3seconds 0.5 mm   2   1 mm 5 mm Hg   1 second   1 mm 3 1.5 mm 1 mm Hg 0.5seconds   5 mm Hg(*Note: A similar table can be hypothetically constructed taking intoconsideration cavity wall expansion, instead of contraction.)

In context with routine endoscopic procedures the above mentionedhypothetical situation associated with serial number 2 is mostacceptable out of the three hypothetical examples because a highmagnitude cavity wall movement excursion is not at all desirable while amoderately high transient pressure surge may be acceptable in mostendoscopic procedures. Thus the nuisance value of a cavity wall movementexcursion is relatively more than the nuisance value of the saidtransient pressure surge. However the amplitude of the pressure surgeshould also be not very high because it may promote intravasation andother problems.

Thus while selecting the diameter of the constriction site two thingsare kept in mind, the operational needs of the endoscopic procedure asalready explained in this paragraph and the anticipated cavity wallcontraction and expansion movements. Thus in those endoscopic procedureswhere mechanical stability of the cavity walls is important thenumerical value of the constriction site diameter D should be relativelysmaller. Thus in context with FIG. 5, the fact that slope of curve 3 isrelatively less does not make it an ideal curve for all endoscopicprocedures because there may be endoscopic precedures where mechanicalstability of the cavity walls is the major concern and in such casecurve 1 or 2 could be ideal to follow.

Limiting and Predicting Cavity Pressure Surge in Case of AccidentalOutflow Obstruction:

If an abnormally high pressure develops inside a tissue cavity duringendoscopic surgery it may cause mechanical rupture of the cavity and mayalso lead to dangerous intravasation. Referring to FIG. 1 if duringendoscopic surgery the outflow tube is accidentally blocked the cavitypressure does not increase to dangerous levels because the controllerautomatically instructs the pump 5 to work at a reduced inflow flowrate, thus a surgical complication is avoided. Referring to the systemshown in FIG. 2 if the outflow tube 12 is accidentally blocked thecavity pressure rises to a dangerously high value in the absence of acontroller. In context with FIG. 2 an accidental obstruction of theoutflow tube or a deliberate obstruction of the inflow tube as achievedby willfully closing the inflow port, both the situations result in asteeply rising pressure as measured by the transducer 17. Thus, whileusing the mechanical version of the invention as shown in FIG. 2, it issuggested that before starting the endoscopic surgery the surgeon shoulddeliberately blocks the distal end of the inflow tube 10 by closing theinflow port of the endoscope and note the resultant maximum pressurerise. If the resultant pressure is higher than the maximum prescribedsafe cavity pressure, then the diameter of the constriction site can beincreased by some magnitude such that the resultant pressure created byblocking the inflow tube is well below the maximum safe pressureprescribed for the tissue cavity. In this manner, for a mechanicalsystem as shown in FIG. 2, for a specific inflow rate, the maximumresultant pressure that would develop inside the cavity in the case of ablock in the outflow tube can be predictably known and limited. Suchmethod of knowing and limiting the rise in cavity pressure as a resultof outflow tube obstruction does not have much role in the controllerbased version of the invention as shown in FIG. 1. However, even if thecontroller based version of the invention as shown in FIG. 1 is beingused and a high out flow rate is being used then if the outflow tube issuddenly obstructed a transient pressure surge of a relatively small orlarge amplitude may be experienced before the controller finallystabilizes the inflow pump rotation speed at a significantly reducedvalue to maintain the initially desired preset cavity pressure. Suchpressure surge occurs because initially the pressure transducer sensesan exponentially increasing cavity pressure, next a correspondingfeedback signal is sent to the controller and the controller finallyacts by reducing the rotational speed of the inflow pump and all theseactions may take a few seconds to be implemented, especially if theinflow pump was operating at a very high speed of rotation, and in thisshort time interval a transient surge in the cavity pressure may beexperienced. The amplitude of such pressure surge would be small due tothe controller feedback mechanism but even a small magnitude surge maydamage fragile tissues, for example tissue inside a brain tissue cavity.The amplitude of the said surge can be predictably reduced by suitablyincreasing the value D. Thus a relatively higher value of D enhancespatient safety by predictably limiting the maximum pressure which candevelop inside the cavity in case of an accidental obstruction of theoutflow tube 12 if the mechanical version of the invention is being usedand it also predictably limits the amplitude of any small amplitudepressure surge which might occur when the inflow tube is accidentallyblocked while the controller based version of the invention is beingused. It has been described in the previous paragraph that theoperational efficiency of the system also improves if the value of D isincreased. Thus a suitable value of D can be selected by keeping intoconsideration patient safety and system efficiency. Once a suitablevalue for D is selected it never altered thereafter as has already beendiscussed previously. The systems shown in FIGS. 1 and 2 can also havethe provision of incorporating multiple constriction sites havingdifferent diameters D to suit and accommodate the operational needs ofmultiple type of endoscopic procedures.

Methods of Shortening the Cavity Refilling Time:

The advantage of shortening the cavity refilling time has already beendiscussed in paragraph 32 and in the present invention this beneficialmaneuver can be carried out by the help of the controller. Referring toFIG. 1, one simple way of reducing the cavity refilling time is bytemporarily increasing the fluid flow rate into the cavity while thecavity is being filled. The physical principals related to the saidmaneuver shall now be described. Referring to FIG. 1 let the differencein the values of R1 and R2 be denoted by a value R which can be statedin equation form as R=R1−R2. Also R1 has to be always more than R2 ifany positive cavity pressure is to be maintained. In the system shown inFIG. 1 it is seen that if the cavity pressure is fixed at a preset valueP then the value R=R1−R2 also never changes irrespective of the desiredoutflow rate. The value D is always fixed as already discussed. Thisimplies that in the normal operational mode, for any fixed value of P,the value R=R1−R2 always remains the same. However, when the inflow portis deliberately closed the pressure transducer senses an increasedpressure due to which the inflow rate is significantly reduced by thepressure feedback circuit, the outflow rate being always fixed at avalue R2. In a mathematical manner it can be stated that if the inflowport is deliberately closed the value

R reduces while the pressure value P remains unchanged. A certainminimum reduction in the value R associated with an unchanged P canserve as a trigger which prompts the controller to carry out a specifiedsequence of events. Let such trigger be termed as ‘refilling initiationtrigger’. The controller can be so programmed such that upon beingprompted by the ‘refilling initiation trigger’ the controller can carryout any one of the below mentioned three maneuvers A, B or C:

-   1. Maneuver A: The moment the controller is prompted by a ‘refilling    initiation trigger’ the controller makes the pump 5 to work at some    increased flow rate such that a pressure P1, which usually would be    higher than the desired cavity pressure, is created and maintained    in the inflow circuit proximal to the blocked inflow port. The value    of P1 is so selected that when the inflow port is opened after    reintroducing the endoscope the cavity gets completely filled up in    a desired shorter time interval and at the end of such a maneuver    the cavity pressure also should not exceed a prescribed maximum safe    cavity pressure or a lower value as desired by the surgeon.    Subsequent to opening the inflow port the pressurized fluid    accumulated in the inflow circuit enters the cavity in the form of a    transient high velocity jet lasting for a few seconds, due to which    the cavity gets filled at an accelerated pace thus reducing the    total refilling time. The cavity refilling time can thus be reduced    by programming the controller to create and maintain a suitable    higher value of P1 but it is also important that the value P1 should    be low enough such that at the end of the refilling phase, that is    when the cavity is completely filled, the pressure inside the cavity    does not exceed the maximum prescribed safe cavity pressure. The    moment the inflow port is opened the pressurized fluid enters into    the cavity and pressure transducer immediately senses a fall in    pressure below P1. The controller has to be further programmed that    such that any further fall in pressure below P1 should serve as a    second trigger which prompts the controller to start working in the    normal mode. By normal mode it is meant that the controller    functions in order to maintain a desired cavity pressure at a    desired outflow rate as was initially decided at the beginning of    the surgery. The only draw back in this proposed method of reducing    the cavity refilling time is that an accidental kinking of the    outflow tube 12 may be wrongly sensed by the controller as    deliberately blocking the inflow port. But such accident can be    avoided by fixing a suitable upper limit for the cavity pressure or    to just accept the remote possibility of such a remote accident but    the maximum cavity pressure created in such an eventuality is known    and can also be limited. Some hypothetical numerical examples shall    be taken in order to further clarify the steps proposed in this    paragraph. It is practically seen in hysteroscopy that if the value    P1 is taken as 160 mm Hg a uterine cavity having a volume capacity    about 20 ml gets filled in approximately 2 seconds and at the end of    which a uterine cavity pressure of 60 mm Hg is created. If the    cavity had been allowed to fill at a normal flow rate used in actual    surgery, for example 50 ml/minute, it would have taken 24 seconds to    completely fill a cavity having the same volume capacity. However if    a bladder cavity having a large volume capacity of up to 300 ml is    substituted in place of the uterine cavity the proposed ‘method A’    cannot be used for reducing the cavity refilling time. Methods B and    C are being proposed to reduce the cavity refilling in the case of    large cavities like bladder cavity.-   2. Method B: Let us take a hypothetical example of a bladder cavity    having volume capacity of 300 ml and the desired cavity pressure    while doing the endoscopic surgery being 30 mm Hg. As explained in    method A the controller is programmed to create a pressure P1 when    the inflow tube is deliberately blocked after withdrawing the    endoscope. In method A the opening of the inflow port after again    introducing the endoscope into the cavity, serves as the second    trigger for the controller to start working in the normal    operational mode to maintain a desired cavity pressure and at a    specified outflow rate but in method B the controller is programmed    differently such that opening the of inflow port after again    introducing the endoscope into the cavity should serve as the second    trigger which prompts the controller to work at an increased flow    rate for a specified time, such time being the calculated time    interval in which the cavity would get completely filled, and after    the expiry of such specified time the controller being further    programmed to start working the system in the normal operational    mode. Taking an hypothetical example with numerical values, if the    value P1 was taken as 160 mm Hg, as was assumed in method A, then 20    ml fluid shall accumulate inside the bladder cavity in 2 seconds but    still 280 ml=300 ml-20 ml more fluid needs to be introduced inside    the bladder cavity in order to fill it completely. Hypothetically,    the controller may be so programmed that opening of the inflow port    should serve as a second trigger to the controller to make the    inflow pump 5 work at an inflow rate of 1000 ml/minute for 16.8    seconds. At such flow rate 280 ml fluid can be pushed into the    bladder cavity within 16.8 seconds. Had the bladder cavity been    filled at an inflow rate of 50 ml/min it would have taken 6 minutes    for the cavity to get completely filled where as by resorting to    method B the cavity filling time is reduced to 18.8=2+16.8 seconds.-   3. Method C: Let the ‘refilling initiation trigger’ serve only as a    trigger which informs the controller that the inflow port has been    deliberately blocked and the controller should be so programmed that    it allows the inflow pump to continue working in the normal    operational mode, that is to maintain the desired cavity pressure.    The opening of the inflow port can serve as the second trigger which    prompts the controller to make the inflow pump work at an increased    flow rate for a specified time and then to again start working in    the normal operational mode. This would reduce the cavity refilling    time significantly. Taking a hypothetical example similar to the    example taken in method B, if opening the inflow port serves as a    trigger to make the inflow pump work at a flow rate of 1000 ml/min    for 18 seconds then the bladder cavity would get completely filled    in 18 seconds.

It is to be noted that in this paragraph the term ‘inflow rate’ is notthe true actual rate which fluid enters into the cavity via the inflowtube because some amount of fluid is also constantly escaping via theopening in the constriction site 8. But the fluid escaping via theopening in the constriction site 8 is very small, especially during theinitial part of the cavity refilling phase, thus it can be neglected.Thus in this paragraph the term ‘inflow rate’ made be deemed to implythe actual cavity inflow rate.

Measurement of the Actual Cavity Pressure:

In the system shown in FIG. 1 and FIG. 2, the value P refers to theactual fluid pressure inside the cavity 18, but in reality P is apressure value which is sensed by the transducer 17 in the inflow tube,such as at a point 6 which is situated in the upstream part of theinflow tube 10, far away from the cavity. In any system the mostconvenient place for installing the pressure transducer is inside themain pump housing. As already discussed in paragraph 29 a transducerlocated in such position may not measure the actual pressure inside thecavity. However in the proposed invention the pressure P measured by thesaid transducer is only negligibly higher that the actual cavitypressure thus the pressure measured by the said transducer may beconsidered to represent the actual cavity pressure. In context withdetermining the actual cavity pressure three experiments were carriedout and these experiments are described in the following paragraphs.

‘Experiment 1’ to Show that ‘P’ is Only Negligebly Higher than theActual Cavity Pressure:

Experiment 1 was conducted to demonstrate that the pressure value Pmeasured by the transducer 17 can be considered to represent an almosttrue cavity pressure, from the surgical point of view. The layout ofexperiment 1 is similar to the system shown in FIG. 2 except that theinner diameter and length of the inflow and out flow tubes has beenspecified and in this experiment the cavity pressure has also beenmeasured directly. In experiment 1 the inflow tube 10 is a two meterlong rubber tube having an internal diameter of 5 mm, the out flow tube12 is also a two meter long rubber tube having an inner diameter of 5 mmand the tissue cavity has been substituted by a rigid spherical cavityhaving approximately the same volume capacity, that is 25 ml, as that ofa normal uterine cavity. In this experiment fluid pressures, P2 and P3,have been measured at two different locations by varying the out flowrate R2 between 0 to 600 ml/minute. Let P2 represent the pressure whichis measured at a point located high up in the up stream portion of theinflow tube 10, such as point 6. This pressure P2 is measured by thealready existing transducer 17. Let P3 represent the actual pressureinside the experimental cavity pressure which is measured directly byinserting a tube into the said experimental cavity and by attaching atransducer at the distal open end of this tube. The transducer and theseparate tube which is inserted into the experimental cavity formeasuring the actual cavity pressure P3 is not shown in any diagram andhas only been hypothetically assumed. Let the difference between P2 andP3 be represented by a value P.diff. This expression can be written inthe equation form as P.diff=P2−P3. Experiment 1 was carried out bykeeping R2 at seven different values ranging between 0 to 600 ml/minuteand the value P.diff was measured for each of the seven values of R2.Also, during the entire experiment 1 the P2 was maintained approximatelyat 60 mm Hg by suitably increasing or decreasing the flow rate of theinflow pump 5 and the value 60 mm Hg was so chosen as such a pressurevalue is commonly maintained in endoscopic procedures, however in suchan experimental setup the actual value of P2 does not seem to influencethe result of experiment 1 which is shown in table 14. TABLE 14 R2P.diff (ml/minute) (mm Hg) 0 Zero 50 Zero 130 Zero 230 Zero 400 Zero 5002 600 6

It is evident that for the outflow rate between 0 to 400 ml/minute thevalue P.diff is so small that it had not been possible to elicit itexperimentally. At an out flow rate of 500 ml/minute P.diff was found tobe 2 mm Hg while at an outflow rate of 600 ml/minute the value of P.diffwas 6 mm Hg. Most endoscopic surgeries are done and can be done atoutflow rate ranging between 0 to 400 ml/minute and higher flow ratesare needed rarely. Even the value 2 mm Hg for P.diff, which is seen atan outflow rate of 500 ml/minute is small enough to be neglected fromthe surgical point of view. Thus for endoscopic surgeries which are donebelow 500 ml/minute outflow rate the value P.diff may be consideredzero, for all practical purposes.

Experiment 2:

In experiment 1 it is clear that the value P.diff is negligibly smallfor outflow rates below 500 ml/min. The values P.diff were so small thatthey could not be determined experimentally.

However in context with experiment 1 a mathematical relationship betweenR2 and P.diff can only be derived if the values of P.diff are somehowdetermined experimentally. Thus it was decided to use a 20 meter longtube so that resistance to fluid flow is adequate enough to make itpossible to determine the values P.diff via experimental means. For thisan experiment 2 was carried out.

The layout for experiment 2 is similar to experiment 1 except that theinflow tube 10, the experimental cavity 18 and the outflow tube 12, allthree items were replaced by a single tube 20 meter long, having aninternal diameter of 5 mm and extending between the inflow and theoutflow pumps. In experiment 2 the pressures P2 and P3 were measured atthe proximal part of this 20 meter long tube very near to the outlet endof the inflow pump 5 and at the distal end of this 20 meter tube verynear to the inlet end of the outflow pump 14. The experiment wasconducted utilizing similar steps as in experiment 1. The results ofexperiment 2 are given in table 15 which is as follows: TABLE 15 R2 P.diff (ml/minute) (mmHg) 0 0 50 4 130 10 230 18 400 42 500 44 600 50

Referring to table 15 the values of R2 were plotted on the X axis of agraph and the values for P.diff were plotted on the Y axis of the graphand the resultant curve 8 is shown in FIG. 8.

At least in the range of R2 between 0 to 600 ml/min the curve 8 can beconsidered to be a straight line curve.

For values of R2 greater than 600 ml/min this curve may become nonlinear but that is not relevant with respect to endoscopic surgery wheregenerally flow rates greater than 600 ml/min are seldom required. Thecurve 8 can be represented by a mathematical expression R2=A=P.diffwhere ‘A’ is a constant. In context with table 13 the values of P.diffcan be determined empirically by utilizing more sensitive experimentalmeans and the said determined values of P.diff and R2 in the range 0 tp600 ml/min can be fed into the controller and the controller can beprogrammed in a manner that the value P.diff is automaticallysubstracted from the perceived value P, thus the actual cavity pressureis always displayed. In this manner the controller always displays andworks at the actual cavity pressure which is determined after takinginto consideration the value P.diff as just explained. Thus it can beconcluded that the system of the present invention as shown in FIG. 1can display and work at the actual cavity pressure, irrespective of theoutflow rate. It is being possible to determine the actual cavitypressure in the described manner because in the present invention theout flow rate remains constant all through the surgery and is neverallowed to vary. If the out flow rate continuously fluctuates as in theprior art systems, the true cavity pressure cannot be measured in themanner just described because irregular variations of the outflow rateare always associated with irregular accelerations and de accelerationsof the inflow rate which lead to irregular fluctuations in the valueP.diff which does not allow the value P.diff to be measured by themethod just described. It may be concluded that in the present inventionthe surgeon may work at any outflow rates and still know the actualcavity pressure in an extremely reliable manner.

Experiment 3:

Experiment 3 was carried out to show that the pump 14 which isincorporated on the out flow side of the irrigation circuit alsocontributes towards reducing the value of P.diff for any same outflowrates. Experiment 3 was carried out using the same experimental setup asused in experiment 1, except that the outflow pump 14 was removed, theoutflow tube 12 was made to directly drain into the waste fluidcollecting reservoir 16 at atmospheric pressure and the constrictionsite 8 was fully occluded. In experiment 3, R2 is equal to R1 thus thevalue R1 is being substituted in place of R2. In experiment 3 the valuesP.diff were calculated for different values of the inflow rates. Thefindings of experiment 3 are stated in table 16 which is as follows:TABLE 16 R1 P. diff (ml/minute) (mmHg) 0 0 50 4 130 6 230 8 400 10 50012 600 14

By comparing the results of experiment 1 and experiment 3 as given intables 14 and 16 it is clear that by removing the outflow pump thepressure fall between any two points in the irrigation circuit isreduced. In physical terms it can be stated that by the system of theproposed invention fluid can be transported at a reduced pressuregradient for the same flow rate. A proposed explanation to theseexperimental observations is that in the proposed invention the fluidflow is somehow acquiring the characteristics of a laminar or streamlineflow which is helping in reducing the turbulence in the fluid flow.Though non scientific but it may even be proposed that the fluid in theirrigation circuit is not actually flowing but is being carried enmassby the help of two peristaltic pumps. It may also be proposed that thetwo peristaltic pumps by consumption of energy are reducing the fluidturbulence. It may also be proposed that the fluid inside the cavity isnot actually flowing but is being displaced, the inflow pump pushes somevolume in the cavity while the outflow pump simultaneously extracts thesame volume of fluid from the cavity. It may also be proposed the systemof the proposed invention is somehow contributing by reducing theReynold number for the flow path. It may also be proposed that the twoperistaltic pumps, by the consumption of energy, are somehow reducingthe cavity turbulence because theoretically if turbulence is produced bythe consumption of energy then it should also be possible to negateturbulence by the consumption of energy.

Experiment 4: Demonstrates the Effects of Introducing Constrictions inthe Irrigation Circuit on The Value P.diff:

In paragraph 61 the inner diameter of the inflow tube, the inflow port,the outflow port and the out flow tube were considered to be uniformlythe same and the same has been maintained till now. In routineendoscopic setups it is frequently seen that the diameter of the inflowport is smaller than the diameter of the inflow tube which can beconsidered as a constriction in the inflow tube, because the inflow tubeand the inflow port are in continuity with each other. Experiment 4 wascarried out in order to demonstrate the effect of such a constriction onthe value P.diff and the steps and the basic layout for experiment 4being similar to experiment 1. Experiment 4 consists of multiple steps.First, the inner diameter of the inflow port was reduced from 5 mm to 2mm with all other factors remaining unchanged and the experimentalfindings are given in table 17 which is as follows: TABLE 17 R1 P. diff(ml/minute) (mmHg) 0 Zero 50 Zero 130 Zero 230 Zero 400 1 500 3 600 7

Next, the inner diameter of the inflow port was maintained at 2 mm butthe inner diameter of the out flow port was also reduced to 2 mm and bydoing so the experimental findings were found to the same as depicted inthe above table 17. Next, the inner diameters of the inflow and the outflow ports were maintained at 2 mm respectively but the inner diameterof the outflow tube was increased from 5 mm to 10 mm and theexperimental findings were still the same as shown in table 17. Thus thefindings of experiment 4 reveal that the by introducing a constrictionin the inflow tube the value P.diff increases by a small magnitude whichdepends on the magnitude of the constriction diameter. Such effect ofintroducing a constriction in the inflow circuit on the value P.diff mayeither be ignored from the practical point of view or such effect may betotally negated by suitably programming the controller as previouslydescribed by utilizing the equation R2=A×P.diff. In this manner even inthe presence of constrictions inside the inflow tube the controller canbe programmed to display and work at the actual cavity pressures. Fromexperiment 4 it is inferred that even if the diameter of the outflowport is reduced but its value is not made lower than the inflow portdiameter, the value P.diff does not change. From experiment 4 it is alsoinferred that increasing the diameter of the outflow tube or the outflowport does not affect the value P.diff. Certain endoscopic surgeries arecarried out utilizing miniature endoscopes which have inflow and outflowports of significantly reduced diameters and in such cases the valueP.diff may be appreciably high to be ignored especially at high outflowrates. In such cases it would be extremely useful to negate the effectof P.diff as already described. Thus in the present invention it ispossible to continuously determine the actual cavity pressures even if aminiature endoscope is used.

Intraoperatively Switching Between Two or More Types of IrrigationFluids:

The concept of switching between two or more types of irrigation fluidsduring an endoscopic procedure has been described in a previousparagraph entitled ‘Intraoperatively switching between two types ofirrigation fluids’. This concept relates to a maneuver in which a ‘firstfluid’ contained inside the irrigation circuit consisting of the inflowtube and the tissue cavity is replaced by a ‘second fluid’ in arelatively short time and such being achieved by flushing the saidinflow circuit with the ‘second fluid’ till the point where a desiredminimum purity threshold level for the second fluid is achieved. Asalready explained the minimum purity threshold is the minimumconcentration of sodium ions in the second fluid at the end of theflushing phase at which monopolar or bipolar electrosurgery can becarried out. Also as previously discussed a relatively short flushingtime is desirable as it reduces the total surgical time and this can beachieved by temporarily increasing the flow rate through the irrigationcircuit provided the cavity pressure does not increase during suchmaneuver because a high pressure may cause the tissue cavity to burst.Taking a hypothetical example let the total volume capacity of theirrigation circuit consisting of the inflow tube and the tissue cavitybe equal to a value V which implies that the total volume of the firstfluid contained in the said irrigation circuit is V. If the saidirrigation circuit is to be flushed by an equivalent volume V of thesecond fluid in time T then the second fluid needs to flow through theirrigation circuit at a rate which is equal to V divided by T. If aminimum threshold purity of the second fluid is not attained in time Tthen flushing flow rate can be suitably increased. Let R.flush be theflow rate at which if the irrigation circuit is flushed for a time Tthen at the end of such flushing a minimum acceptable threshold purityis attained inside the second fluid. R.flush is obviously a high flowrate and if the second fluid is pushed into the inflow tube at such ahigh flow rate it may cause mechanical rupture of the tissue cavity or asudden intravasation due to a high pressure which is created inside thecavity by such an act. It has been clearly described previously in theparagraph entitled ‘Cavity pressure or the outflow rate, both can bealtered independently without varying the value of the other parameter’that if the outflow rate and the inflow rate are increased or decreasedby the same magnitude the cavity pressure does not vary. Assuming ahypothetical situation that the system shown in FIG. 1 working at inflowrate R1 and outflow rate R2 generates a cavity pressure P and the systemis to be flushed at a higher flow rate ‘R.flush’. If the outflow rate inthis assumed hypothetical situation is increased to R.flush and theinflow rate is also simultaneously increased by a magnitude R.flush−R2which implies that the value of the inflow rate is made equal toR1+(R.flush−R2) then the cavity pressure P shall not change. Thecontroller 17 can be programmed that by a single command the out flowrate is increased from R2 to R.flush and the inflow rate is increasedfrom R1 to R1+(R.flush−R2) for a time T. It may be argued that duringsuch an act if the outflow tube gets accidentally blocked the cavitypressure may increase to a dangerously high level and such an accidentcan be avoided by the pressure feedback mechanism wherein the controllercan be additionally programmed that during the cavity flushing phase ifan increased cavity pressure is sensed then the said process of cavityflushing is to be immediately stopped. It may also be argued that inFIG. 1 only a single fluid source reservoir 1 and a single fluid supplytube 2 is shown then how it would be possible to deal with two differenttypes of fluids in the system shown in FIG. 1. Such problem can beeasily solved by incorporating two separate fluid reservoirs containingdifferent fluids along with two separate suction tubes and suitableclamps capable of blocking the lumen of the suction tubes can beattached to the suction tubes. The clamps can work electromechanicallyunder the influence of the controller such that the clamp related to theright type of fluid opens subsequent to a flushing command being givento the controller and the other clamp keeps the lumen of the secondsuction tube closed. In FIG. 1 the second fluid reservoir and the secondsuction tube have deliberately not been shown only to keep the drawingsimple. Thus in the proposed invention it is possible to switch betweentwo different types of irrigation fluids intraoperatively by temporarilyincreasing the flushing flow rate in such a manner that the cavitypressure does not vary during the said flushing maneuver. The proposedinvention has obvious use in hysteroscopic surgery, arthroscopic surgeryand TURP surgery. The proposed invention can also be utilized forcarrying out endoscopic procedures in the brain and the spine. Brainendoscopic surgery also known as neuro endoscopy is a frequentlyperformed life saving procedure. The human brain has got cavities knownas the brain ventricles. Many endoscopic procedures are performed byinserting the endoscope into the brain ventricles and many suchprocedures utilize continuous flow irrigation. Endoscopic surgery of thespine is also a frequently performed and many endoscopic proceduresrelated to the spine utilize continuous flow irrigation. The proposedinvention can be useful in other endoscopic procedures also whichrequire continuous flow irrigation. The present invention can be usefulin certain non endoscopic procedures also where a tissue cavity needs tobe distended by continuous flow irrigation such as phako emulsificationand vitrectomy procedures which are related to the eye ball cavity.

The advantage of predicting the required volume for the irrigation fluidat the beginning of the surgery has already been explained. Suchmaneuver though extremely simple is extremely helpful. In the presentinvention the outflow rate remains fixed all through the surgery unlessintentionally changed by the surgeon. The average total surgical timefor similar endoscopic procedures usually does no vary and the surgeonson the basic of their past experience always have an idea of theapproximate time which an endoscopic procedure takes. Such timemultiplied by the outflow rate R2 gives a fairly accurate idea of thetotal volume of irrigation which would be consumed in the proposedendoscopic procedure if intravasation was to be ignored and the surgeonsagain by their past experience also have a fairly rough idea of the ofthe volume of fluid which is intravasated in a certain duration of timefor specific endoscopic procedures. In this manner the total fluid thatwould be required in a particular endoscopic procedure can be roughlyevaluated but even such rough evaluation is helpful as explained in aprevious paragraph entitled ‘Predicting the total volume of requiredirrigation fluid’. It is advisable to take a slightly greater volumethan that predicted by the method described in this paragraph.

The proposed invention can also be used to impart endoscopic trainingskills by the help of endoscopic experimental models based on thepresent invention. Also use and scope of the present invention is notlimited to human tissue cavities and it may be used for performingmultiple endoscopic procedures in animal tissue cavities also and alsofor imparting training in endoscopic surgeries related to animal tissuecavities.

It is believed that the foregoing description conveys the bestunderstanding of the objects and the advantages of the presentinvention. It will be understood by those skilled in the art thatnumerous improvements and modifications may be made to the embodimentsof the invention disclosed herein without departing from the departingfrom the spirit and scope thereof.

The Invention is Unique

There is no other prior art system in which two peristaltic pumpsrunning simultaneously at fixed flow rates predictably create andmaintain any desired fixed pressure inside a tissue cavity, despiteunpredictable irregular physiological contractions of the cavity walls,for any precise and fixed outflow rate for unlimited time such that theinstantaneous real time rate of fluid intrvasation is constantly known.Besides many other unique features of the invention are stated havealready been stated above.

The Heart and Soul of the Invention

The constriction site 8 as described in the manuscript is the heart andsoul of the invention without which the invention cannot exist.

The inventors have published a research paper entitled ‘A simpletechnique to reduce fluid intravasation during endometrial resection’ inthe Feburary 2004 issue of the Journal of the American Association ofGynecologic Laproscopists (see reference 6 i.e. Kumar A, Kumar A: Asimple technique to reduce fluid intravasation during endometrialresection. The journal of the American Association of GynecologicLaproscopists 11(1): 83, 2004). In this study endometrial resectionswere performed in 539 women using the system of the present invention.During the endometrial resections excess fluid intravasation weredetected and prevented from occurring in 20 cases using the feature ofthe system of the proposed invention which enables the surgeon to alwaysknow the instantaneous real time rate of fluid intravasation. Also inall these 539 the inventors could resect the intramural part of thetubal openings successfully in a prospective manner only because of thepredictably stable mechanical distension provided by the system of theproposed invention. Such findings have not been published in the past,possibly because such a maneuver is not possible with any of the priorart systems.

The inventors have published another research paper entitled‘Endometrial Tuberculosis’ in the February 2004 issue of the Journal ofthe American Association of Gynecologic Laproscopists (see reference 7i.e. Kumar A, Kumar A: Endometrial Tuberculosis, The Journal of theAmerican Association of Gynecologic Laproscopists 11(1): 2, 2004). Inthis study two high quality images of endometrial tuberculosis have beenpublished. It is important to note that it was possible to obtain suchhigh quality images only because the uterine cavity wall could achieveabsolute mechanical stability and the uterine cavity pressure could bemaintained at a precise stable desired value by using the system of theproposed invention. As of today, besides this study, no other image isavailable in which the caseous tubercular deposits have beenphotographed. It is evident that the negligible fluid turbulenceprovided by the system of the proposed invention prevented such depositsfrom being washed away.

The inventors have published another research paper entitled‘Microcolpohysteroscopy’ in the May 2004 issue of the Journal of theAmerican Association of Gynecologic Laproscopists (see reference 8 i.e.Kumar A, Kumar A: Microcolpohysteroscopy. The Journal of the AmericanAssociation of Gynecologic Laproscopists 11(2): 131, 2004). In thisstudy, in one of the images it is even possible to see the microvesselsinside the microvilli related to the endocervical canal. It is notpossible to photograph such minute structures like microvessels unlessthe cavity wall exhibits absolute mechanical stability which wasprovided by the system of the proposed invention.

HIGH RESOLUTION, SHARP & HIGH MAGNIFICATION IMAGES were possible to bephotographed from the inside of the uterine cavity only due to the lessturbulence and predictably stable mechanical distension possible by theproposed invention. Few such images are shown in FIG. 10 and are theyare explained herebelow:

Image A and B show tubercular deposits over the endometrium in provencases of endometrial tuberculosis. The said tubercular deposits could bephotographed only because they were not washed away due to negligibleturbulence.

Images C and D show retrograde menstruation blood coming out of thetubal openings, a fact which has been reported in text literature butnever photographed. These photographs were again possible due to minimalturbulence.

Image E shows the intramural part of the left tubal opening beingresected electrosurgically.

The surgeon can have courage to undertake such maneuver only if apredictably stable mechanical distension of the uterine cavity ispresent.

Image F shows a highly magnified endometrial polyp in the panoramicmode. The afferent and efferent capillary blood vessels of the polyp arealso clearly seen due to. It has been possible to capture this imageonly because of negligible turbulence. Such pedunculated polypscontinuously exhibit swaying movements in a turbulent environment as aresult of which it is difficult to photograph the microvessels with suchclarity.

Advantages of the Proposed Invention

The proposed invention makes endoscopic procedures extremely safe,simple, more accurate and easy to perform. The proposed invention helpsthe surgeons to perform endoscopic surgeries with greater safety andconfidence especially in the initial phase of their learning, curve.Also a distending system based on the proposed invention can be used inmultiple endoscopic procedures thus reducing the financial burden on thehospital and the patient. The advantages of proposed invention aresummarized in the following table along with the correspondingdisadvantages of the prior art systems: ADVANTAGES OF THE UTERINEDISTENDING SYSTEM BASED UPON THE PRESENT DISADVANTAGES OF THE INVENTION:PRIOR ART SYSTEMS: It is possible to create and maintain any desiredThis is not possible in any prior art precise tissue cavity pressure forany desired precise system. fixed outflow rate including a zero outflowrate. The instantaneous real time rate of fluid intravasation Suchfeature is not present in any into the patient's body is constantlyknown without prior art system. using any type of fluid flow ratesensors. The instantaneous real time rate of fluid intravasation This isnot possible in any prior art into the patient's body can be determinedeven system. mechanically without using a controller and any type offluid flow rate sensors. A predictably constant any desired fluidpressure can This is not possible in any prior art be maintained insidea tissue cavity for indefinite system. time. A predictably constant anydesired fluid pressure can This is not possible in any prior art bemaintained inside a tissue cavity for indefinite system. time despitephysiological cavity wall contractions. A predictably constant clearendoscopic visualization This is not possible in any prior art ispossible. system. It is possible to achieve a predictably stable This isnot possible in any prior art mechanical distension of the cavity walls.system. It is possible to maintain any desired precise and high This isnot possible in any prior art cavity pressure without increasing the‘maximum system. possible fluid intravasation rate’. It is possible toeasily and quickly change over from This is not possible in any priorart one type of irrigation fluid to a different type of system.irrigation fluid during an endoscopic procedure in any desired shortperiod of time such that the cavity pressure does not change during suchmaneuver.

CONCLUSION

The proposed invention is novel and unique. The invention relates notonly to increasing surgical efficiency in certain endoscopic proceduresbut it also helps in preventing human morbidity and human mortality inmany endoscopic procedures. Thus the proposed invention is extremelyuseful for entire mankind.

1. A system for distending body tissue cavities of subjects bycontinuous flow irrigation during endoscopic procedures the said systemcomprising: a fluid source reservoir containing a non viscousphysiologic fluid meant for cavity distension; a fluid supply conduittube connecting the fluid source reservoir to an inlet port of avariable speed positive displacement inflow pump and an outlet port ofthe said inflow pump being connectable to an inflow port of an endoscopeinstrument through an inflow tube for pumping the fluid at a controlledflow rate into the cavity, the flow rate of the said inflow pump beingtermed as the inflow rate; an inflow pressure transducer being locatedanywhere in the inflow tube between the outlet port of the inflow pumpand the inflow port of the endoscope; an outflow port of the endoscopebeing connectable to an inlet port of a variable speed positivedisplacement outflow pump through a outflow tube for removing the fluidfrom the cavity at a controlled flow rate, the flow rate of the saidoutflow pump being termed as the outflow rate, an outlet port of theoutflow pump being connected to a waste fluid collecting container, andcharacterized in that a housing tube having a controllable constrictionsite is being provided between the fluid source reservoir and the inflowtube such that the same by-passes the inflow pump; wherein housing tubeprovides a route for any excess fluid being pumped by the inflow pump tobypass the inflow pump and go back to the fluid supply tube or the fluidsource reservoir.
 2. A system as claimed in claim 1, wherein the fluidsource reservoir containing the non-viscous physiologic fluid ismaintained at atmospheric pressure or at a pressure greater than theatmospheric pressure.
 3. A system as claimed in claim 1, wherein aproximal open end of the fluid supply tube is connected to the fluidsource reservoir and a distal end of the tube is connected to the inletport of the variable speed positive displacement inflow pump. 4-25.(canceled)